FOUS30 KWBC 240815
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
415 AM EDT Thu Oct 24 2024

Day 1
Valid 12Z Thu Oct 24 2024 - 12Z Fri Oct 25 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE MIDDLE MISSISSIPPI VALLEY...

Introduced a Marginal Risk for portions of the Middle MS Valley,
from northwest IL and southeast IA into northern MO (and adjacent
portions of far northeast KS). Strengthening southwesterly low-
level flow (850 mb) to 40-50 kts this evening will usher in PWATs
to near 1.25" (well above the 90th percentile, per SPC sounding
climatology), along with sufficient instability (ML CAPE 1000+
J/kg) and forcing (potent shortwave trough crossing the Central
Plains) for convective development. Strong vertical shear (~50
kts) with idealized curving hodographs will likely favor discrete
convection (with both the mean flow and bunkers right vectors
favoring storm motions of 20-30 kts), and despite relatively low
PWs (particularly compared to warm season convection) any
supercells will likely be capable of 1-2"/hr rainfall rates (per
40-km neighborhood HREF probabilities for 1"/1-hr exceedance of
40-50%). While 1-2" totals should be well tolerated by soils (and
largely beneficial, given dry antecedent conditions), localized
training could result in too much rainfall (2"+) too quickly (in a
matter of 2-3 hours). Given this threat, an isolated instance or
two of flash flooding is possible.

Churchill


Day 2
Valid 12Z Fri Oct 25 2024 - 12Z Sat Oct 26 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Churchill


Day 3
Valid 12Z Sat Oct 26 2024 - 12Z Sun Oct 27 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Churchill
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FOUS30 KWBC 280809
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
409 AM EDT Mon Oct 28 2024

Day 1
Valid 12Z Mon Oct 28 2024 - 12Z Tue Oct 29 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Campbell


Day 2
Valid 12Z Tue Oct 29 2024 - 12Z Wed Oct 30 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Campbell


Day 3
Valid 12Z Wed Oct 30 2024 - 12Z Thu Oct 31 2024

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FROM THE
SOUTHERN PLAINS TO THE UPPER MISSISSIPPI VALLEY/UPPER MIDWEST...

A mid-level trough is expected to eject into the Plains by
Wednesday morning. Surface troughing will help Gulf moisture to
lift northward ahead of an approaching cold front. Cooler air
filtering in from the west/north will encounter the warm air
advection associated with the low-level jet. Showers and
thunderstorms are expected to increase in coverage and intensity
across the central portion of the country; which in turn will
increase the potential for heavy rainfall and local areas of
concern for flooding. The inherited old Day 4 Marginal Risk area
was maintained with minor expansions across portions of Texas and
across Iowa, Minnesota and Wisconsin to reflect the latest WPC QPF
and model trends. At this point there appears to be two distinct
areas of concentration for the heaviest QPF. The first near the
juncture of Oklahoma, Texas and Arkansas state borders and the
second near the juncture of eastern Iowa, southern Wisconsin and
northern Illinois. Given the current FFG guidance and drier
antecedant conditions, a Marginal still seems most appropriate for
the level of risk. Should newer guidance continue to trend higher
an embedded Slight Risk may need to be considered as the event gets
closer.

Campbell
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FOUS30 KWBC 290824
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
424 AM EDT Tue Oct 29 2024

Day 1
Valid 12Z Tue Oct 29 2024 - 12Z Wed Oct 30 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Campbell


Day 2
Valid 12Z Wed Oct 30 2024 - 12Z Thu Oct 31 2024

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FROM THE
SOUTHERN PLAINS TO THE UPPER MISSISSIPPI VALLEY/UPPER MIDWEST...

During this period a mid-level trough is expected to eject into
the Plains by Wednesday morning, and in turn, surface troughing
will draw Gulf moisture northward ahead of an approaching cold
front. Cooler air filtering in from the west/north will encounter
the warm air advection associated with the low-level jet.
Convection over the region is expected to increase in both coverage
and intensity. The Storm Prediction Center as highlighted a Slight
Risk for severe storms for portions of the Plains and Mississippi
Valley. This favorable setup will also increase the potential for
heavy rainfall and local areas of concern for flooding.

There continues to be two distinct areas swaths of higher QPF. The
first remains focused near the juncture of Oklahoma, Texas and
Arkansas state borders amid areas of higher instability. The second
area continues to have a run-to-run westward trend and is now spans
from northeast Kansas to north-central Wisconsin near the stronger
height falls. With this westward shift the Marginal Risk area was
altered in shape to reflect this trend and as such reduced/removed
portions of the eastern boundary from Illinois, eastern Iowa and
Missouri while expanding further into Nebraska, west-central Iowa
and southeast Minnesota and central Wisconsin Very dry antecedent
conditions should help minimize any threat (ergo, current FFG
guidance values are high), but a Marginal Risk outline still seems
appropriate for this lead time with room to adjust with future
guidance (including the CAM guidance).

Campbell


Day 3
Valid 12Z Thu Oct 31 2024 - 12Z Fri Nov 01 2024

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF
THE LOWER MISSISSIPPI VALLEY...

The upper level trough will continue to advance through the Upper
Midwest which will send the cold front through the eastern portions
of the Southern Plains and mid-Mississippi Valley. Strong to
severe thunderstorms will persist for areas along and ahead of the
advancing frontal boundary per SPC (Marginal Risk); which will
shift the heavy rain potential to the central Gulf Coast to
western Kentucky where there is a Marginal Risk area for excessive
rainfall. Areal averages will be in the 1 to 2 inch range with
locally higher amounts possible.

Campbell
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FOUS30 KWBC 300822
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
422 AM EDT Wed Oct 30 2024

Day 1
Valid 12Z Wed Oct 30 2024 - 12Z Thu Oct 31 2024

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FROM THE
SOUTHERN PLAINS TO THE UPPER MISSISSIPPI VALLEY/UPPER MIDWEST...

Convection over the region is expected to increase in both
coverage and intensity with the set up becoming more favorable for
isolated heavy rainfall amounts/rates and localized flooding
concern. Showers and thunderstorms in the vicinity to Oklahoma,
Texas and Arkansas state borders will have local enhancement amid
areas of higher instability. There has been a persistent westward
shift from run-to run guidance in regards to the placement of the
higher QPF across the Plains and Upper Mississippi Valley/Upper
Midwest, but general consensus is favoring a concentration across
north- central Iowa into southeast Minnesota and western Wisconsin
where the greatest height falls are located and fastest
acceleration of low level flow. This will enhance local rainfall
efficiency and boost amounts. Deterministic guidance suggests 1 to
3+ inches across this area.

Antecedent conditions are quite dry- as reflected by the very high
flash flood guidance. That should mitigate any widespread threat
of excessive rainfall as well as progressive cells. Even so, the
Marginal Risk area still seemed appropriate based on what the
magnitude of the instability and mesoscale forcing from the coarser
numerical guidance with room to adjust with future guidance
(including the CAM guidance).

Campbell/Bann


Day 2
Valid 12Z Thu Oct 31 2024 - 12Z Fri Nov 01 2024

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF
THE LOWER MISSISSIPPI VALLEY...

As the upper level trough advances through the Upper Midwest the
surface front will makes its way into the Southern Plains and Mid-
Mississippi Valley. Instability is expected to remain the highest
in portions of the Lower Mississippi Valley while the flow
pattern/mesoscale forcing weakens farther north. Convection is
expected to initiate along and ahead of the cold front by late
morning and increase coverage during the afternoon hours across the
Lower Mississippi Valley and into the Lower Ohio Valley. Areal
averages will be in the 1 to 2 inch range with locally higher
amounts possible.

Campbell


Day 3
Valid 12Z Fri Nov 1 2024 - 12Z Sat Nov 02 2024

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF
THE SOUTHERN ROCKIES AND SOUTHERN PLAINS...

Another trough will move inland across the West as ridging stays in
place over much of the South. Warm Gulf moisture will be advecting
northward through the High Plains. Meanwhile, the strongest
instability will likely be in place over West Texas and eastern new
Mexico. Areal coverage of thunderstorms is forecast to increase
during the overnight hours into portions of the Texas panhandle,
Oklahoma and far southern Kansas. Per SPC, the environment will be
conducive for large hail and there is a Marginal Risk in effect for
severe weather. There is also the potential for excessive rainfall
near eastern new Mexico and West Texas/Panhandle and there is a
Marginal Risk area in effect for the threat of isolated areas of
flooding.

Campbell

d
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FOUS30 KWBC 010810
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
410 AM EDT Fri Nov 1 2024

Day 1
Valid 12Z Fri Nov 01 2024 - 12Z Sat Nov 02 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR A SMALL PORTION
OF SOUTHEASTERN NEW MEXICO...

...New Mexico and the TX/OK Panhandles...

A digging trough over the intermountain west will begin to tap into
building Gulf moisture across eastern New Mexico and the Texas and
Oklahoma Panhandles. With interactions with upper level energy,
CAMs guidance is highlighting the Slight risk area from the
Sacramento Mountains to the Texas state line for the heaviest
rains. The whole area has been very dry in recent weeks (as has
most of the country), so that should greatly mitigate the flash
flooding threat. Further, the guidance isn't in perfect agreement
on where the heaviest rains will occur...though the Slight risk
highlights where most of the guidance is. Thus...the threat is most
certainly still on the lower end of the Slight risk scale.

The storms that form over New Mexico will train northeastward
across the Panhandles. Where repetitive training can occur,
isolated flash flooding is possible, but the storms will be
stronger further south and west.

...Louisiana/Mississippi...

A convergence zone is likely to set up across the Mississippi Delta
Friday night. Slow moving convection is expected, though that
convection would likely need to move over an urban or flood
sensitive area to cause localized flash flooding. With HREF
probabilities for 3 inches of rain Friday night over 50%, a
Marginal Risk area was added with this update.

Wegman


Day 2
Valid 12Z Sat Nov 02 2024 - 12Z Sun Nov 03 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
SOUTHERN PLAINS...

Additional Gulf moisture will track north on a LLJ across Texas and
into the Slight Risk area on Saturday. PWATs may exceed 1.75
inches. The trough over the intermountain west will slow to a
crawl, while much faster moving shortwaves round the base of the
trough and move north up the Plains. Multiple rounds of storms are
expected from north Texas to the Kansas City metro. The heaviest
rains are likely across central Oklahoma, where a higher-end Slight
is in place.

As on Day 1, extremely dry antecedent conditions are in place over
much of the Slight Risk area, with soil moisture levels from Nasa
Sport at under 10%. While clay soils may start out hydrophobic, for
the most part, the empty creeks and streams should work to prevent
much flash flooding. Given the available moisture for the storms to
work with, training is likely, which should raise the flash
flooding potential to widely scattered. The Slight Risk area was
expanded a bit towards the northeast and now approaches the Kansas
City metro. Meanwhile a portion of north Texas was removed based on
the latest guidance. Nonetheless a slower forward progression of
the entire pattern should concentrate the worst impacts from any
flash flooding in a smaller corridor highlighted by the Slight
Risk. No major changes were made to the inherited risk areas. The
greatest uncertainty is how well the dry soils will absorb the
sudden abundance of moisture as the drought conditions in place now
across the southern Plains will help in many cases to mitigate any
potential flooding impacts.

Wegman


Day 3
Valid 12Z Sun Nov 03 2024 - 12Z Mon Nov 04 2024

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
EASTERN OKLAHOMA AND THE OZARKS...

The inherited Moderate Risk area was shifted to the southeast a few
rows of counties in Oklahoma with this update. This is in response
to the latest guidance suggesting the heaviest rainfall will
fall more across eastern Oklahoma through the Ozarks of western
Missouri. A big factor as to the flooding potential will be
rainfall from the Day 2/Saturday period, which alone is expected to
result in a widespread 3-5 inches of rain across the Moderate Risk
area. When added to the 2-4 inches of rain expected Sunday for many
of the same areas, even the antecedent drought conditions in place
now should not be able to handle two consecutive days of heavy
rain. The primary point of uncertainty is how much overlap there
will be between the two days. The slow moving nature of the entire
system should mean much of the Moderate Risk area will be in the
overlap. Urban and flood sensitive areas are likely to have the
greatest risk of impacts from training storms, with the strongest
storms and heaviest rains expected Sunday night. The storms will
continue north and east across northern Missouri and into Iowa and
Illinois, where the Slight Risk was extended based partially on
prior days' rainfall. Regardless, outside of the Moderate Risk
area, antecedent dry conditions will have a bigger mitigating
impact on the flooding.

Wegman
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FOUS30 KWBC 011555
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1155 AM EDT Fri Nov 1 2024

Day 1
Valid 16Z Fri Nov 01 2024 - 12Z Sat Nov 02 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR A SMALL PORTION
OF SOUTHEASTERN NEW MEXICO...

16Z Excessive Rainfall Outlook Discussion...
No changes needed to either the Slight/Marginal risk areas
southeast New Mexico and adjacent portions of the Texas/Oklahoma
panhandles or with the Marginal risk area along the immediate Gulf
coast. With trough amplification over the western United States now underway...flow across the Gulf coast region should begin to
back...allowing for moisture to return northward/westward leading
to expanding coverage over the southern High Plains late tonight.
Dry antecedent conditions should mitigate the risk of excessive
rainfall in most areas...with the biggest exception being in
southeast New Mexico which remains hydrologically sensitive
following significant flash flooding less than 2 week ago. So made
no changes to the Slight Risk area that was already in place...and
only minor nudges to the perimeter of the Marginal risk area.
Farther east...the HREF continues to suggest additional convection
is possible later today that will have the potential for isolated
rainfall rates of 1 inch per hour...and even a low probability of 2
inch per hour rates immediately west of Lake Pontchartrain late
this afternoon/early evening. So no significant change made with
that Marginal risk area.

Bann

...New Mexico and the TX/OK Panhandles...

A digging trough over the intermountain west will begin to tap into
building Gulf moisture across eastern New Mexico and the Texas and
Oklahoma Panhandles. With interactions with upper level energy,
CAMs guidance is highlighting the Slight risk area from the
Sacramento Mountains to the Texas state line for the heaviest
rains. The whole area has been very dry in recent weeks (as has
most of the country), so that should greatly mitigate the flash
flooding threat. Further, the guidance isn't in perfect agreement
on where the heaviest rains will occur...though the Slight risk
highlights where most of the guidance is. Thus...the threat is most
certainly still on the lower end of the Slight risk scale.

The storms that form over New Mexico will train northeastward
across the Panhandles. Where repetitive training can occur,
isolated flash flooding is possible, but the storms will be
stronger further south and west.

...Louisiana/Mississippi...

A convergence zone is likely to set up across the Mississippi Delta
Friday night. Slow moving convection is expected, though that
convection would likely need to move over an urban or flood
sensitive area to cause localized flash flooding. With HREF
probabilities for 3 inches of rain Friday night over 50%, a
Marginal Risk area was added with this update.

Wegman

Day 2
Valid 12Z Sat Nov 02 2024 - 12Z Sun Nov 03 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
SOUTHERN PLAINS...

Additional Gulf moisture will track north on a LLJ across Texas and
into the Slight Risk area on Saturday. PWATs may exceed 1.75
inches. The trough over the intermountain west will slow to a
crawl, while much faster moving shortwaves round the base of the
trough and move north up the Plains. Multiple rounds of storms are
expected from north Texas to the Kansas City metro. The heaviest
rains are likely across central Oklahoma, where a higher-end Slight
is in place.

As on Day 1, extremely dry antecedent conditions are in place over
much of the Slight Risk area, with soil moisture levels from Nasa
Sport at under 10%. While clay soils may start out hydrophobic, for
the most part, the empty creeks and streams should work to prevent
much flash flooding. Given the available moisture for the storms to
work with, training is likely, which should raise the flash
flooding potential to widely scattered. The Slight Risk area was
expanded a bit towards the northeast and now approaches the Kansas
City metro. Meanwhile a portion of north Texas was removed based on
the latest guidance. Nonetheless a slower forward progression of
the entire pattern should concentrate the worst impacts from any
flash flooding in a smaller corridor highlighted by the Slight
Risk. No major changes were made to the inherited risk areas. The
greatest uncertainty is how well the dry soils will absorb the
sudden abundance of moisture as the drought conditions in place now
across the southern Plains will help in many cases to mitigate any
potential flooding impacts.

Wegman

Day 3
Valid 12Z Sun Nov 03 2024 - 12Z Mon Nov 04 2024

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
EASTERN OKLAHOMA AND THE OZARKS...

The inherited Moderate Risk area was shifted to the southeast a few
rows of counties in Oklahoma with this update. This is in response
to the latest guidance suggesting the heaviest rainfall will
fall more across eastern Oklahoma through the Ozarks of western
Missouri. A big factor as to the flooding potential will be
rainfall from the Day 2/Saturday period, which alone is expected to
result in a widespread 3-5 inches of rain across the Moderate Risk
area. When added to the 2-4 inches of rain expected Sunday for many
of the same areas, even the antecedent drought conditions in place
now should not be able to handle two consecutive days of heavy
rain. The primary point of uncertainty is how much overlap there
will be between the two days. The slow moving nature of the entire
system should mean much of the Moderate Risk area will be in the
overlap. Urban and flood sensitive areas are likely to have the
greatest risk of impacts from training storms, with the strongest
storms and heaviest rains expected Sunday night. The storms will
continue north and east across northern Missouri and into Iowa and
Illinois, where the Slight Risk was extended based partially on
prior days' rainfall. Regardless, outside of the Moderate Risk
area, antecedent dry conditions will have a bigger mitigating
impact on the flooding.

Wegman
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FOUS30 KWBC 020814
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
414 AM EDT Sat Nov 2 2024

Day 1
Valid 12Z Sat Nov 02 2024 - 12Z Sun Nov 03 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE SOUTHERN PLAINS...

A deep but slow-moving longwave trough will move across the Desert
Southwest through tonight. Multiple shortwaves of upper level
energy will move through the jet stream rounding the base of the
trough. As those shortwaves eject over the high Plains of Texas and
Oklahoma, they will meet up with increasing Gulf moisture tracking
northward across Texas. At the surface, the trough-ridge interface
will feature a slow-moving cold front which will also add to the
forcing in the area. PWATs will increase above 1.75 inches across
much of the Slight Risk area.

The combination of the increasing moisture and ample low and upper
level forcing will be multiple rounds of training thunderstorms
initiating over northwest Texas and the Panhandle, then quickly
organize into segments which will slowly track east as embedded
heavier cells track northeastward and roughly parallel to the
lines. This will support training convection which in addition to 2
inch per hour rates, could mean any particular location in the
Slight Risk area could see multiple rounds of heavy rainfall.

In contrast to the heavy rains, mitigating the flood risk has been
multiple weeks of very little rain across the middle of the
country. The dry streams and creekbeds will easily be able to
handle most of the rain that falls, but should training of multiple
storms occur, especially over any urban areas such as Oklahoma
City, then flash flooding impacts could quickly arise. Since the
storms will be slow moving, this will support widely scattered
flooding impacts, especially from Wichita Falls, TX through
Oklahoma City.

Wegman


Day 2
Valid 12Z Sun Nov 03 2024 - 12Z Mon Nov 04 2024

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FROM CENTRAL AND
NORTHEASTERN OKLAHOMA AND ALONG THE KANSAS/MISSOURI BORDER...

Storms from the overnight period Saturday night will diminish with
daytime heating and the typical daytime weakening of the LLJ.
However, throughout the day the atmosphere will recharge such that
by Sunday night the passage of another shortwave will result in a
refiring of the storms across central and eastern Oklahoma, which
will grow and train upscale into far eastern Kansas, Missouri, and
eventually Iowa and far western Illinois. The Moderate Risk was
largely unchanged, with a small northward expansion. This is
primarily the portion of the region which is expected to get some
rain tonight, which will prime the soils for the heavier rains for
most of eastern Oklahoma and points north and east by Sunday night.
This expected overlap of rainfall is what will push the flash
flooding impact and coverage potential into the Moderate Risk
category, albeit the lower end of the category. Obviously this will
largely depend on how much rain is seen in the Moderate Risk area
Saturday night before the start of the period.

Once again the LLJ off the Gulf will supply a stream of ample
moisture to the slow-moving storms, so the flooding impact
potential, especially in areas where Sunday is the first
significant rains seen in the area in weeks, will be dependent on
the upper level energy tracking along the surface front keeping
storms moving over the same areas. The ERO risk areas were
conservative on the north and east sides and more liberal on the
south and west sides due to expected prior rainfall (or lack
thereof) on Saturday. The lack of prior rainfall has gotten river
levels to very low conditions, making plenty of room for the water
from heavy rain. This will greatly diminish the flooding threat
broadly. Had there been recent rains in this area, then a more
expansive Moderate Risk may have been needed. From Day 2 onward the
flooding potential across the middle of the country will be highly
dependent on how well previous days rains were able to result in
flooding, as amounts in the highest rainfall risk areas will be
largely the same day to day, so overlap with previous' days will be
critical. Of course, urban and low-lying/flood prone areas will be
at greater risk of flash flooding through Sunday night.

Wegman


Day 3
Valid 12Z Mon Nov 04 2024 - 12Z Tue Nov 05 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM NORTHEAST
TEXAS THROUGH THE CHICAGOLAND AREA...

The slow moving cold front that will have brought rains to areas
west of the Mississippi this weekend will move a little faster to
the east Monday and Monday night. Additional lines of storms are
expected again on Monday, but mostly for areas not expected to get
too much rain this weekend. Thus, the Slight Risk remains good as
the flooding from heavy rain is offset by the dry soil conditions.
By this point we should have a good idea as to how much flooding
will be seen as both Saturday and Sunday's forecast rains will be
on repeat over the Slight Risk area again on Monday. No significant
changes were made or needed from the inherited Day 4 forecast.

Wegman
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FOUS30 KWBC 030808
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
308 AM EST Sun Nov 3 2024

Day 1
Valid 12Z Sun Nov 03 2024 - 12Z Mon Nov 04 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
SOUTHERN PLAINS AND THE OZARKS...

...Southern Plains and the Ozarks...

In coordination with TSA/Tulsa, OK; LZK/Little Rock, AR; and
SGF/Springfield, MO forecast offices, the inherited Moderate Risk
area was downgraded to a Slight with this update. The surrounding
Marginal was trimmed out of Wisconsin, Minnesota, and much of Iowa.

There was a notable south and eastward shift in the guidance as to
the axis of heaviest rainfall expected across Oklahoma and Arkansas
today into tonight. A longwave trough over the Southwest will shift
eastward today. Embedded shortwave disturbances as well as a
developing 90 kt jet streak will move over the region through
tonight. A well-established low level jet (LLJ) will continue to advect plentiful Gulf moisture northward into the area. The result will be
multiple rounds of storms with embedded training cells in OK/AR and
into MO. Much of the area has been very dry lately, though
yesterday some rain impacted the area, especially in Oklahoma and
into southern Missouri. Multiple "streaks" of much heavier rainfall
are anticipated where cells of much heavier rain train over the
same areas. This is likely to cause widely scattered to scattered
instances of flash flooding.

Antecedent conditions will be the primary limiting factor keeping
the flooding impacts in check. Very dry conditions prior to this
event has led to drought conditions developing with very low river
and stream levels. Thus...much of the rain expected today will be
beneficial and work to return those rivers and streams to much more
normal levels. However, given the plentiful moisture, training
storms, and some flood prone areas, the heavy rain could cause
localized flash flooding. The eastward shift in the guidance has
also introduced the Ozarks into the highest risk area. The
topography of the area will help to focus the heavy rainfall into
the valleys...which could result in rapid river, stream and creek
rises. This also locally increases the flash flooding threat as
compared to the same amount of rain falling over relatively flat
terrain.

While forecast rainfall amounts haven't changed appreciably as
compared with previous forecasts, the shift of the heaviest rain
eastward and into many areas that did not receive appreciable rain
today has reduced the likely flood impact threat as well as
coverage. When added to the dry antecedent conditions, this should
keep flooding impacts from becoming widespread enough to reach
Moderate Risk levels. Hence, while flash flooding remains likely as
amounts could locally exceed 5 inches, the impact and coverage was
determined to be in the Slight Risk category...hence the downgrade.

...Upper Midwest...

In the upper Midwest, the eastward shift in the guidance and a more
west to east movement of the expected convection should limit how
much instability and moisture reach the upper Mississippi Valley.
It's likely any remaining convection will be in a much weakened
state by the time the rain reaches this area. Since similarly dry
conditions and drought have impacted the upper Great Lakes in
recent weeks, the largely stratiform nature of the rain should mean
all of the rain will be beneficial with no flooding concerns noted.
Thus, the Marginal was trimmed towards the south.

Wegman


Day 2
Valid 12Z Mon Nov 04 2024 - 12Z Tue Nov 05 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM NORTHEAST
TEXAS THROUGH PORTIONS OF WESTERN LOWER MICHIGAN...

Few changes were made or needed to the Slight Risk area across the
middle of the country.

A deep longwave trough will continue move eastward but begin to
weaken and lift northward back into the jet stream on Monday. As it
does so, associated jet streaks will intensify downstream of the
trough, which will support its deamplification. The LLJ that has
been supplying Gulf moisture will also elongate towards the north
reaching as far north as lower Michigan by Monday. This will cause
the resultant moisture to focus in a SSW to NNE corridor from Texas
to Michigan. Unidirectional SSW flow will support training
thunderstorms. The strongest storms are expected from Texas through
Missouri, which will have access to the greatest Gulf instability
and moisture. The storms will gradually weaken the further north
you go, but are expected to maintain their integrity into Wisconsin
and Michigan. The topography of the Ozarks will further locally
enhance rainfall totals due to some upslope support.

Due to overlap with the rainfall footprint Monday with that
expected today, there is some potential for a Moderate Risk upgrade
from western Arkansas into southern Missouri. However, this will be
highly dependent on how much rain falls in that area today/Sunday.
Total rainfall amounts will be somewhat lower on Monday as compared
to Sunday, hence the importance of rain falling over the same areas
as Sunday to enhance the flooding threat to Moderate Risk levels. Thus,
the potential for an upgrade will continue to be evaluated.

Wegman


Day 3
Valid 12Z Tue Nov 05 2024 - 12Z Wed Nov 06 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE MISSISSIPPI AND OHIO VALLEYS...

By Tuesday, a progressive cold front pushing across the Mississippi
Valley and associated upper level trough and shortwave will
separate...with the upper shortwave ejecting northeastward into the
Great Lakes, leaving the front behind. The combination of steady
forward movement of the storms through the day followed by the
rapid diminishing of any and all upper level support by Tuesday
night will rapidly diminish the flooding threat as storm coverage
and intensity also diminish. With some supply of Gulf moisture
continuing on Tuesday, the storms that form through the day will
still have enough punch to cause locally heavy rainfall. However,
the eastward progression of the front should allow this rain to
fall largely over areas that remain dry today/Sunday and Monday.
Antecedent dry conditions will preclude much of the flooding threat
by Tuesday, so only isolated flash flooding in urban and flood
prone areas is anticipated. The Marginal Risk is largely unchanged
from previous forecasts.

Wegman

$$
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FOUS30 KWBC 040808
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
308 AM EST Mon Nov 4 2024

Day 1
Valid 12Z Mon Nov 04 2024 - 12Z Tue Nov 05 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM EASTERN TEXAS
THROUGH WESTERN LOWER MICHIGAN...

...Changes...

Only a few modest changes were made to the inherited forecast.
There was a small southward nudge to the axis of heaviest rainfall
around Lake Michigan, so the Slight risk area was trimmed some in
Wisconsin and northern Lower Michigan in favor of a slightly
expanded Slight in eastern Illinois and far northwestern Indiana.
With some rain in portions of southeast Texas around Houston today,
the expectation of feeder cells into the main plume of moisture,
showers and storms further north warranted a small southward
extension of the Slight to near Houston.
A small Marginal risk was added to portions of east central New
Mexico.

...Texas to the Great Lakes...

A progressive trough over the Plains will continue tracking
eastward towards the Mississippi Valley today. Plentiful shortwave
energy and a strengthening southerly jet streak out ahead of the
trough will both work to increase forcing across the entire Slight
Risk area. The greatest lift and heaviest rainfall is expected from
far southeastern Oklahoma northeast to around St. Louis. Since this
area crosses the heart of the Ozarks, any upslope enhancement will
locally increase rainfall rates. The topography of the area may
also focus the flash flood potential in the valleys, further
increasing the risk of impacts. Plentiful Gulf moisture moving
north on a 40 kt LLJ will run into a developing surface low over
the Plains. As this moisture runs ahead of the NE-moving low the
combination of forcing and topography will enhance rainfall rates.
While there has been some rain in this area from eastern Oklahoma,
Arkansas, and southern Missouri, the heaviest rainfall amounts have
generally been west of where the heaviest rains are expected today.
This fact should mitigate the flood potential and impact somewhat.
Nonetheless, 2 days of heavy rain with rates to 3 inches per hour
in the strongest cells shows no signs of abating for today with all
the aforementioned ingredients still in place. The progressive
nature of the trough and resultant storms should also lessen the
flood risk just a little. Thus, the Slight Risk inherited for this
region continues to look good and no upgrades were considered. This
corridor is highlighted in an internal higher-end Slight.

Further south across Texas, there will be plentiful moisture but
the forcing will both be transient and largely missing this area.
Some rain fell today around Houston, so the threat is in the lower
end Slight range as any storms that form, while isolated to widely
scattered, will be capable of those higher end 3 inch per hour
rates, which especially over any flood prone urban areas could
cause flooding problems quickly.

Meanwhile further north towards Lake Michigan, plentiful forcing
will be in place but both instability and moisture amounts will be
decreasing with latitude. Thus, expect more stratiform rain across
this region...with much lower chances of the higher end rates. That
said, the rain should be longer duration than the heavier rain
further south, and for the Chicagoland area here too there will be
urban considerations which bump the risk level into the Slight
range.

...New Mexico...

A leeside low currently over south central New Mexico will track
northeast as several mesolows work to consolidate into a dominant
single low over Texas and Oklahoma late today. With peak heating,
some wraparound moisture and modest instability over an area with
modestly depressed FFG values, steady rain with some convective
cells ongoing over the area by this afternoon could result in an
isolated flash flooding threat, particularly over any burn scars or
other flood sensitive areas. Thus, a small Marginal Risk area was
added with this update. Precipitation will be ongoing further north
and into the mountains of southern Colorado but temperatures there
will be cold enough for most if not all of the precip to fall as
snow, precluding any flash flooding risk.

Wegman


Day 2
Valid 12Z Tue Nov 05 2024 - 12Z Wed Nov 06 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE MISSISSIPPI AND OHIO VALLEYS...

No changes were made to the inherited Marginal Risk area.

The upper level trough responsible for the past few days of heavy
rain across the southern and central Plains will finally retreat
back into the broader jet into Ontario and Quebec. The upper level
energy supporting the corridor of storms will continue supporting
storms across the Mississippi and Ohio Valleys Tuesday and into
Tuesday night respectively. As the energy lifts north, it will mark
the end of persistent heavy rain and storms from south to north.
Thus, the flooding threat will be more in the morning in Texas, and
more towards the night for the Ohio Valley. Training lines of
storms will move across the Mississippi Valley for much of the day.
These storms will be capable of heavy rains which may cause
isolated flash flooding, especially in any urban areas such as
Memphis. By Tuesday night, weakening of the storms and the shift
well away from any prior days' rain footprint will effectively end
the flooding threat.

Wegman

Day 3
Valid 12Z Wed Nov 06 2024 - 12Z Thu Nov 07 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE SOUTHEAST...

Very few changes were needed to the inherited forecast.

Deep tropical moisture will have overspread all of Florida and will
be advancing into GA and SC at the start of the period Wednesday
morning. A lingering front over the Southeast may act as a focus
for convection across GA and SC as the deep tropical moisture moves
north into the front. Potential Tropical Cyclone Eighteen (PTC18)
is expected to move into the Gulf from Cuba and the northwest
Caribbean as well. For the Florida Peninsula, much of the flooding
threat will be determined by the eventual track of PTC18. The
latest guidance has kept the center of PTC18 far enough west over
the Gulf that despite shear pushing much of the rain associated
therewith to the eastern side of the circulation, it will still
largely remain offshore. However, with PWATs above 2.25 inches, it
won't take much for daily convection to produce heavy rainfall
almost anywhere in the state.

A bullseye of heavier rain is currently forecast across central GA
into SC. While the focus for the heavier rain will be the stalled
out front, there is considerable uncertainty as to instability,
which will greatly determine how strong any storms can get which
could cause flooding. For now it appears much of the rain in GA/SC
will be spread out through Wednesday and into Wednesday night,
which should easily be handled by the antecedent dry conditions.
Thus, the Marginal for this area remains in place with only minor
tweaks made. The area will continue to be monitored for a potential
Slight upgrade, which may not take much given the abundance of
tropical moisture any storms would have to work with.

Wegman

$$
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FOUS30 KWBC 050824
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
324 AM EST Tue Nov 5 2024

Day 1
Valid 12Z Tue Nov 05 2024 - 12Z Wed Nov 06 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
LOWER TO MID MISSISSIPPI AND LOWER OHIO VALLEYS...

A cold front tracking east across the middle of the country is
expected to stall out generally along the Mississippi and Ohio
Rivers late tonight. Southerly flow off the Gulf will continue
pumping plentiful moisture into the front. Meanwhile, in the upper
levels, a large longwave trough over the west will establish itself
as a positively tilted trough by tonight as it digs southwestward
over the Southwest. Before it does so, the last potent shortwave of
the "old" trough will race northeastward into the Great Lakes as
the leading edge of the trough becomes a roughly straight line
southwesterly from the Southwest right through into eastern
Canada.

The potent shortwave and associated surface low will both race
northeastward through the period. While they're over the upper
Mississippi Valley, they will move the front currently stalled from
Texas through Michigan eastward a bit to align with the Slight and
Marginal Risk areas along the Mississippi and Ohio Rivers. This
will give the hard hit northwestern Arkansas region a break as the
heaviest rain shifts east. However, by tonight, both features will
be well into the Great Lakes and Canada, so the forcing pushing
them east will quickly diminish, resulting in another stall-out of
the front. With continuous Gulf moisture, another round of training thunderstorms is expected up the Mississippi and lower Ohio Rivers
tonight. Given both the prior history of this front stalling as
well as urban concerns in the Memphis area especially, a Slight
Risk area was introduced with this update.

Despite the stalled out front keeping the rainfall largely confined
to a narrow corridor, the upper level forcing quickly weakening
tonight should hold rates and coverage in check much better tonight
as compared to the ongoing storms over Texas, Arkansas and Missouri
right now. Thus, forecast rainfall amounts are considerably lower
today and tonight than yesterday. The Slight is considered a
"lower-end Slight" with any flash flooding impacts expected to be
largely confined to low-lying flood prone areas and urban areas.
Like areas further west, this area has also been very dry prior to
this rainfall, so it will still take a prolonged period of heavy
rainfall to result in flash flooding.

Wegman


Day 2
Valid 12Z Wed Nov 06 2024 - 12Z Thu Nov 07 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
GEORGIA AND SOUTH CAROLINA...

A large plume of deep tropical moisture will overspread all of
Florida and move into Georgia and South Carolina on Wednesday and
Wednesday night. This same plume is home to T.S. Rafael down in the
Caribbean. PWATs will increase to as high as 2.25 inches, meaning
the storms expected to form will have plenty of moisture to convert
to heavy rainfall. The front over the Ohio Valley is unlikely to
play too much of a role in the storms over Georgia and South
Carolina. Rather, the guidance suggests a secondary front will from
at the leading edge of the moisture plume that will likely be
enhanced by the right entrance region of the upper level jet
streak, as well as possibly some upslope component (especially in
South Carolina). Regardless of the primary lifting mechanism, there
is good agreement in the guidance for an area of 3 to 5 inches of
rain (though likely much higher amounts will be embedded) in the
Slight Risk area, which is a small increase in amounts from the
previous forecast.

As with areas further west the past several days, this area has
also been incredibly dry lately, with many areas not having seen
appreciable rain in a month. For the swampy and sandy areas, this
will mean it will take a lot of rain before runoff converts to
flooding. Further north across interior SC and GA, the clay soils
are likely quite hydrophobic due to the recent dry weather, which
will notably increase runoff once the heavy rain gets started.
Thus, locally increased impacts are possible. An internal higher-
end Slight area was introduced for the peak rainfall area of east-
central Georgia and west central South Carolina for this potential.

Since this plume is home to T.S. Rafael, this would be considered a
predecessor rain event (PRE) if Rafael were to head towards the Big
Bend and GA/SC. However, since the latest forecasts keep Rafael
tracking westward in the Gulf this rainfall event is not considered
a PRE.

Wegman


Day 3
Valid 12Z Thu Nov 07 2024 - 12Z Fri Nov 08 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE SOUTHEAST AS WELL AS FOR PORTIONS OF THE SOUTHERN PLAINS...

...Southeast...

The cold front over the Appalachians that will drive the Day
2/Wednesday rainfall event will move southward to coastal South
Carolina and southern Georgia Thursday and Thursday night. The
southerly flow of deep tropical moisture ahead of the front will
abate somewhat in favor of a more neutral easterly flow. This will
keep periods of heavy rain going...but both less widespread, less
persistent, and less heavily. The core of heaviest rain will shift
to the coast of SC/GA and north FL, but since most of this area is
likely to not have seen substantive amounts of rain on Wednesday,
and the coastal swamps can usually handle a lot of rainfall with
few problems, have opted to keep the area in a Marginal Risk for
this update. However, recent model trends have been for the
heaviest rain to increase with time as the CAMs move into this
period of time. Should that happen a Slight Risk will likely be
necessary.

...Southern Plains...

A potent upper level low will begin to eject out of the Southwest
and into the southern Plains on Thursday. A strong cold front will
develop as a result with plentiful snow into much of northeastern
New Mexico. This area was trimmed from the Marginal Risk with this
update. For the rest of the Marginal Risk area, some Gulf moisture
will be captured and advected northward across north Texas and
Oklahoma, but amounts will be somewhat limited. With only broad
forcing from an upper level jet streak but few coherent features
away from the strong cold front, the rainfall footprint will be
broad and disorganized. This area has seen plentiful rainfall over
the past few days, so the additional rainfall, while not much, may
still cause isolated instances of flash flooding.

Wegman

$$
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FOUS30 KWBC 060823
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
323 AM EST Wed Nov 6 2024

Day 1
Valid 12Z Wed Nov 06 2024 - 12Z Thu Nov 07 2024

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE SOUTHEAST...

In coordination with CAE/Columbia, SC and FFC/Peachtree City, GA
forecast offices, a Moderate Risk upgrade was introduced with this
update.

A plume of deep tropical moisture, indirectly associated with
Hurricane Rafael will continue overspreading portions of the
Southeast today. The moisture plume will run into a developing
front over Georgia and South Carolina. An upper level jet streak
will add lift to the atmosphere. Late today into this evening, the
nocturnal low level jet's strengthening will kick the moisture
advection into high gear. Frontogenesis occurring over Georgia and
South Carolina will act to focus the heavy rain over the narrow
Moderate Risk corridor. Expect training convection to develop
during the evening which will persist through the overnight and
while slowly weakening in the pre-dawn hours, is likely to continue
into western South Carolina into Day 2/Thursday.

HREF probabilities show a 20 to 25 percent chance of a 100 year
rainfall event in the Moderate Risk area. FFGs are very high in the
area due to recent dry conditions with only very light rain. This
has likely made some of the clay soils quite hydrophobic. The
hydrophobic soils will likely increase the runoff from the heavy
rain, which will likely quickly exceed FFGs as the heavy rain
likely persists for multiple hours.

Wegman


Day 2
Valid 12Z Thu Nov 07 2024 - 12Z Fri Nov 08 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
SOUTHEAST AS WELL AS FOR MUCH OF THE TEXAS PANHANDLE AND WESTERN OKLAHOMA...

...Southeast...

Heavy rain will be ongoing across Georgia and especially South
Carolina at the start of the period Thursday morning. While the
rainfall will be diminishing in intensity, it's expected after the
much heavier rains of Wednesday night, that the lighter totals
forecast for Thursday will still be influential since antecedent
conditions will be radically different by then as compared to where
they are now. The Slight Risk threat largely is for the Thursday
morning period with lingering rainfall from Wednesday night. Expect
the rain to continue diminishing through the day as the moisture
plume shifts westward with Hurricane Rafael.

...Texas Panhandle and Western Oklahoma...

A positively tilted longwave trough and associated upper level
energy in the form of jet streaks and shortwave energy will support
the development of a strong low over the southern Plains. To the
west, a significant amount of the low's moisture will fall in the
form of snow. Where the precipitation will remain as rain, expect
steady heavy rain across the Texas Panhandle and western Oklahoma.
While rates are not generally expected to be notably heavy, the
flood threat will be primarily focused on the long duration of
steady rain, as well as the fact that much of this area was hit
very hard with heavy rain a few days ago, so soils and rivers
remain elevated in this region. Thus, low FFGs support the Slight
Risk upgrade.

Wegman


Day 3
Valid 12Z Fri Nov 08 2024 - 12Z Sat Nov 09 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
CENTRAL AND SOUTHERN PLAINS...

The upper level low over the Southwest will eject into the Plains
on Friday. There will be significant upper level energy associated
with the low, which combined with strong frontogenesis, plentiful
Gulf moisture advecting up the Plains on the low level jet, and a
strengthening surface low...expect heavier rainfall amounts across
Oklahoma and Kansas on Friday as compared with Wednesday. While
north Kansas didn't see as much rain a few days back compared with
areas further south...much of the rest of the Slight risk area does
overlap with both the heavy rain from a few days ago but continued
rainfall from Day 2/Thursday. Thus, added an internal higher-end
Slight for western Oklahoma into south Kansas. Depending on how
much rain the area gets on Day 2, there is some potential for a
Moderate Risk upgrade in this area with future updates.

Wegman


$$
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FOUS30 KWBC 070820
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
320 AM EST Thu Nov 7 2024

Day 1
Valid 12Z Thu Nov 07 2024 - 12Z Fri Nov 08 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
SOUTHEAST AS WELL AS PORTIONS OF WEST TEXAS AND WESTERN OKLAHOMA...

...Southeast...

Heavy rain continues across Georgia and South Carolina this
morning. A nearly stationary front across the region is acting as a
focus for that rainfall, which due to an influx of tropical
moisture moving into the front from the Atlantic remains stuck. The
moisture running into the front is allowing for convective
development along the front in Florida and Georgia, which then
advect northeastward into South Carolina. While convective coverage
has been slowly diminishing, along with the storms with the
heaviest rainfall, it's likely that the rain will continue into the
day today. The inherited Slight and Marginal risks were largely
left unchanged with this update, as the rainfall is generally
behaving as expected. Since there will be a very slow drift of the
heaviest rainfall towards the South Carolina coast, which due to
the swampy terrain is generally much better equipped to handle
heavy rainfall rates, a Slight Risk is sufficient to cover the
flash flooding threat, rather than a continuation of the Moderate.

...West Texas and Western Oklahoma...

A strong upper level low over the Southwest will interact with an
LLJ of Gulf moisture and a developing surface low forming ahead of
the upper level low. A large area of rain will develop from the
Texas and Oklahoma Panhandles south and east over portions of the
Cap Rock of Texas and much of Oklahoma west of Oklahoma City.
Instability will be a significant limiting factor on short-term
rainfall rates and the strength of any convection, but the fact
that all of those synoptic systems just described will be very slow
moving should increase the duration of steady rainfall. Since much
of this region was hit hard with heavy rain a few days ago, FFGs
remain low enough that they should be overcome in widely scattered
instances in the Slight Risk area, and in isolated instances in the
Marginal Risk region.

Wegman


Day 2
Valid 12Z Fri Nov 08 2024 - 12Z Sat Nov 09 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
SOUTHERN PLAINS...

The upper level low over the Southwest and its attendant surface
low will both continue moving northeast across the Plains on
Friday. With continued influx of Gulf moisture, the typical comma
shaped precipitation footprint will develop from Texas to Oklahoma.
Out west in Colorado and New Mexico the precipitation will be
mostly in the form of snow. Where it remains all rain, the heaviest
rain will be from north Texas across Oklahoma and into south
central Kansas. As today, instability will remain the primary
limiting factor for heavy rain in most areas, as MUCAPE values
generally stay under 1,000 J/kg. For the Slight Risk area, there
has been a general eastward/faster shift in the guidance, but that
will at least be somewhat offset by the rainfall expected today
over the Panhandles and western Oklahoma.

The rationale for the Slight is two-fold. While somewhat lesser
amounts of rain are expected overall for southern Oklahoma and
Texas...greater instability there will favor at least some storms
capable of heavy rainfall in that area. Meanwhile, north of
Oklahoma City, expect a much longer duration rainfall as the
surface low takes its time getting its act together. So while
instantaneous rates will likely be lower than further south, it
will be made up for by the longer duration of the rain.

Wegman


Day 3
Valid 12Z Sat Nov 09 2024 - 12Z Sun Nov 10 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR MUCH OF THE
LOWER MISSISSIPPI VALLEY...

The upper level low that was driving the heavy rainfall the
previous two days will move faster towards the northeast as it
continues its return to the jet stream over the northern tier of
states. The area will still have plenty of moisture from the Gulf
to work with as Rafael (or what's left of it) remains over the
central Gulf but the plume of moisture its embedded in continues to
be drawn north ahead of the surface low's strong cold front. The
front will likely be the dominant forcing for storms in this
region. As on Friday, the southern areas of Louisiana and
Mississippi will have the greater moisture and instability, while
further north FFGs are much lower due to recent heavy rainfall.
Thus, once again the Slight Risk is a two-fold combination of
factors that individually increase the flooding risk. The front
should still be slow enough moving that training storms tracking
north along the front could still cause flooding problems,
especially in Louisiana.

Wegman

$$
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FOUS30 KWBC 080758
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
258 AM EST Fri Nov 8 2024

Day 1
Valid 12Z Fri Nov 08 2024 - 12Z Sat Nov 09 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
SOUTHERN PLAINS...

The upper level low over the Southwest and its attendant surface
low will continue moving northeast across the Plains on Friday.
With a continued influx of Gulf moisture with precipitable water
values of 1.5-2.25" expected near the cyclone's cold front, the
typical comma shaped precipitation footprint will develop farther
up the warm conveyor belt from Texas to Oklahoma which should occur
with precipitable water values at or above an inch. Out west in
Colorado and New Mexico the precipitation will be mostly in the
form of snow. Where it remains all rain, the heaviest rain will be
from north Texas across Oklahoma and into south-central Kansas.
Instability should be sufficient for heavy rain-related issues.

While somewhat lesser amounts of rain are expected overall for
southern Oklahoma and Texas...greater instability there as high as
1500 J/kg of MU CAPE will favor at least some storms capable of
heavy rainfall in that area, with hourly rain totals to 2.5" and
local amounts as high as 6" where cells train. Meanwhile, north of
Oklahoma City, expect a much longer duration rainfall as the
surface low takes its time getting its act together. So while
hourly rain totals will likely be lower than further south, perhaps
1" where slantwise convection/frontogenesis aloft forces greater
precipitation efficiency, it will be made up for by the longer
duration of the rain.

Roth/Wegman


Day 2
Valid 12Z Sat Nov 09 2024 - 12Z Sun Nov 10 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE LOWER MISSISSIPPI VALLEY...

An upper level low will move faster towards the northeast. As
Rafael moves west over the central Gulf, a plume of moisture with
precipitable water values of 1.5-2" gets drawn north ahead of the
surface low's strong cold front. The front will likely be the
dominant forcing for storms in this region. As on Friday, the
southern areas of Louisiana and Mississippi will have the greater
moisture. MU CAPE rises towards 1000 J/kg across parts of LA/MS/TN.
Areas further north have soils which are more saturated/flash
flood guidance is lower. The front should progress slow enough that
training storms tracking north along the front could still cause
flooding problems, especially over portions of LA, MS, and TN.
Hourly rain totals to 2.5" and local amounts of around 6" appear
likely. Lingering disagreement on exactly where the maxima are
expected kept the risk level from being raised to Moderate, though
an upgrade remains possible in future updates should this placement
issue resolve itself and model QPF magnitudes don't back off.

Roth


Day 3
Valid 12Z Sun Nov 10 2024 - 12Z Mon Nov 11 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
PACIFIC NORTHWEST, LOWER MISSISSIPPI VALLEY...TENNESSEE VALLEY...
AND UPPER OHIO VALLEY...

Central Gulf Coast northeast towards southwest Pennsylvania...
Moisture and instability from the Gulf gets advected from the
vicinity of Raphael northeast across portions of the Central Gulf
Coast through the Tennessee and Upper Ohio Valleys. The forward
progress of the front across much of the East should keep any
excessive rainfall concerns minimal -- some of the risk area from
eastern AR to the east-northeast just south of the OH river
accounts for recent rains/some soil saturation. The latest NCEP
and CMC guidance suggests that Raphael gets much closer to the Gulf
Coast than the NHC forecast, which led to avoiding use of the GFS,
NAM, and Canadian guidance explicitly. Since the distance of the
storm from the region at this time frame is unclear, it's also
unclear how high precipitable water values get, though they should
rise above 1.5", particularly in the southern portion of the area
near the coast, which should be enough for heavy rain concerns. It
appears that enough instability could be available along the
immediate Gulf Coast for convection with heavy rainfall. Hourly
rain totals to 2" with local totals to 5" appear achievable along
or near the immediate Gulf coast. Whenever better agreement
amongst the guidance on the future of Rafael as well as the
placement any rainfall maximum near the coast occurs, a Slight
Risk could prove useful at that later time. To the north, hourly
totals up to ~1" with local totals to 2" appear to be the maximum
potential.

Pacific Northwest...
Precipitable water values rise to 0.75-1" with a front moving into
the area. Inflow from the Pacific rises to 50-60 kts from the
south-southwest near the front. In the wake of the front,
instability moves in due to colder air aloft. Hourly rain totals
exceeding 0.5" appear likely here, which would be most problematic
in burn scars. Left the Marginal Risk area intact though simplified
the area's appearance.

Roth

$$
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FOUS30 KWBC 090748
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
248 AM EST Sat Nov 9 2024

Day 1
Valid 12Z Sat Nov 09 2024 - 12Z Sun Nov 10 2024

...THERE IS A HIGH RISK OF EXCESSIVE RAINFALL IN AND NEAR IMPERIAL
CALCASIEU IN LOUISIANA...

An upper level low will move faster towards the northeast. As
Rafael moves west over the central Gulf, a plume of moisture with
precipitable water values of 1.5-2" gets drawn north ahead of the
surface low's strong cold front. The front will likely be the
dominant forcing for storms in this region as it stalls, which have
already begun to evolve in recent radar imagery. The southern
areas of Louisiana and Mississippi will have the greater moisture.
MU CAPE rises to 1000 J/kg or so across parts of LA/MS/TN. Areas
further north have soils which are more saturated/flash flood
guidance is lower. The front should progress slow enough that
training storms tracking north along the front could still cause
flooding problems, especially over portions of LA, MS, and TN.
Hourly rain totals to 2.5" and local amounts of around 8" due to
cell training appear likely based on the 00z HREF probabilities of
8" totals. There is much better agreement on the placement when
compared to this time yesterday. Portions of Central LA have
received 300%+ of their average seven day rainfall, so soils should
have some sensitivity. Coordination with the LCH/Lake Charles LA
forecast office led to the increase to a High Risk.

Roth


Day 2
Valid 12Z Sun Nov 10 2024 - 12Z Mon Nov 11 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
PACIFIC NORTHWEST, LOWER MISSISSIPPI VALLEY...TENNESSEE VALLEY...
AND UPPER OHIO VALLEY...

Central Gulf Coast northeast towards southwest Pennsylvania...
Moisture and instability from the Gulf gets advected from the
vicinity of Raphael northeast across portions of the Central Gulf
Coast through the Tennessee and Upper Ohio Valleys. The forward
progress of the front across much of the East should keep any
excessive rainfall concerns minimal -- some of the risk area from
eastern AR to the east-northeast just south of the OH river
accounts for recent rains/some soil saturation. The guidance
remains unclear as to whether heavy rainfall gets ashore or not.
Precipitable water values should rise above 1.5", particularly in
the southern portion of the area near the coast, which should be
enough for heavy rain concerns. It appears that enough instability
could be available along the immediate Gulf Coast for convection
with heavy rainfall. Hourly rain totals to 2" with local totals to
5" appear achievable along or near the immediate Gulf coast.
Whenever better agreement amongst the guidance on the future of
Rafael as well as the placement any rainfall maximum near the coast
occurs, a Slight Risk could prove useful at that later time. To
the north, hourly totals up to ~1" with local totals to 2" appear
to be the maximum potential.

Pacific Northwest...
Precipitable water values rise to 0.75-1" with a front moving into
the area. Inflow from the Pacific rises to 50-60 kts from the
south-southwest near the front. In the wake of the front,
instability moves in due to colder air aloft. Hourly rain totals
exceeding 0.5" appear likely here, which would be most problematic
in burn scars. Left the Marginal Risk area intact though simplified
the area's appearance.

Roth


Day 3
Valid 12Z Mon Nov 11 2024 - 12Z Tue Nov 12 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
PACIFIC NORTHWEST & CENTRAL GULF COAST...

Central Gulf Coast...
Precipitable water values north of Rafael are expected to remain in
the 1.5-2" range in the vicinity of a slowly progressive front near
the Central Gulf Coast. While much of the guidance keeps rainfall
amounts minimal, the 00z NAM showed local amounts of 3"+, though
it gets there by allowing Rafael to get much closer to the Gulf
Coast than other model guidance. Considering that heavy rainfall
is possible over the previous couple of days, figured a new
Marginal Risk was a sensible precaution in case the NAM is close to
correct and/or soils are saturated by that time.

Pacific Northwest...
Precipitable water values of 0.5-0.75" and MU CAPE of a few hundred
J/kg are expected in a post-frontal environment. Inflow off the
Pacific is expected to remain around 40 kts. Hourly rain totals
exceeding 0.5" remain possible, which would be most problematic in
burn scars. Left the inherited Marginal Risk area intact though
simplified the area's appearance.

Roth

$$
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FOUS30 KWBC 100924
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
424 AM EST Sun Nov 10 2024

Day 1
Valid 12Z Sun Nov 10 2024 - 12Z Mon Nov 11 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS CENTRAL AND
SOUTHWEST LOUISIANA...

Southwest and Central Louisiana...
Moisture and instability from the Gulf gets advected from the
vicinity of Raphael northwest to north across portions of the
Central Gulf Coast through the Tennessee Valley. A slowly
advancing convective complex early this morning across southwest LA
is drifting eastward, showing hourly rain totals to 3" and
isolated totals to 13" thus far over portions of Allen Parish.
There is concern that this complex could hold together past 12z,
which is part of the reason for the upgrade to a Slight Risk, after coordinating with the LCH/Lake Charles LA forecast office.
Additional activity could form behind it closer to a surface
boundary in TX (could be forming at the present time) which is
expected to advect eastward during daytime heating. Moderate Risk
level impacts cannot be ruled out should such thunderstorm activity
persist over recently saturated soils into this afternoon.

Southeast Louisiana...
The guidance broadly remains unclear as to whether heavy rainfall
gets too far ashore southeast LA while mesoscale guidance shows the
complex to the west fizzling as it moves into the region.
Precipitable water values of 1.5-2" Sunday morning across southeast
LA advect offshore with time, which should limit heavy rainfall
concerns. Still, hourly rain totals to 2" and local totals to 4"
are possible on an isolated basis should storms backbuild or train.

Interior Southeast/Mid-South/Tennessee Valley...
The forward progress of the front should keep any excessive
rainfall concerns minimal in areas a bit north of the Gulf Coast
-- some of the risk area from eastern AR to the east-northeast just
south of the OH river accounts for recent rains/some soil
saturation. In this more northern portion of the Marginal Risk
area, hourly totals up to ~1" with local totals to 2" appear to be
the maximum potential. A decent amount of the area within the
Marginal Risk would find the forecasted rainfall welcome.

Changes to continuity were to shave off some of the northeast
portion of the Marginal Risk area, using 00z HREF probabilities of
0.5"+ as a guide, and include some of far southeast Texas to
account for the limited QPF signal there as soils are a bit more
sensitive after the past 24-36 hours of heavy rainfall.

Roth


Day 2
Valid 12Z Mon Nov 11 2024 - 12Z Tue Nov 12 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Roth


Day 3
Valid 12Z Tue Nov 12 2024 - 12Z Wed Nov 13 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL IN AND NEAR
WESTERN WASHINGTON...

Precipitable water values of 0.75-1" advect in as a cold front
approaches, perhaps moves ashore, the Washington and northern
Oregon coast Wednesday morning. Inflow from the Pacific rises to
60 kts at 850 hPa out of the south-southwest with limited
instability available near and behind the front. The ingredients
appear to be there for hourly rain totals of 0.5"+, which would be
most problematic in burn scars. Over the full day, local amounts
of 3-4" are advertised for much of the guidance, which would be
most problematic along the Skokomish river in the Olympic
Peninsula. Enough was there in the guidance for the inherited
Marginal Risk area to remain from continuity; simplified its shape.

Roth

$$
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FOUS30 KWBC 110751
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
251 AM EST Mon Nov 11 2024

Day 1
Valid 12Z Mon Nov 11 2024 - 12Z Tue Nov 12 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

A non-zero chance for flash flooding exists within the far
Southeast Parishes of LA and along the immediate AL/MS coastal
plain as lingering moisture on the northern periphery of the
remnant low from Rafael will persist within the area mentioned
above. Frontal progression to the northwest will slowly sink
southeast with some CAMs initiating a period of stronger boundary
layer convergence that would capable of north-south alignment of
heavier rainfall situated over the Southeast-most Parishes in LA.
The factor that will likely limit the threat will be the lower end
rates between 1-2"/hr max that fall well-below the current FFG
markers located over the proposed impact area. Totals of 2-4" with
locally as high as 6" are depicted within a few of the CAMs, but
it's not a full agreement in the suite neighborhood probabilities
dropping off precipitously for accumulations >3". Decided to retain
the current nil ERO nationally, but wanted to point out the low-
end probability (<5%) for isolated flood concerns in the zone
encompassing the above Parishes to the immediate coastline across
both AL/MS.

Kleebauer


Day 2
Valid 12Z Tue Nov 12 2024 - 12Z Wed Nov 13 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS WESTERN
WASHINGTON AND NORTHWEST OREGON...

The next Atmospheric River will impact the PAC Northwest with an
IVT pulse between 500-800 kg/ms signaling a modest moisture
advection regime that historically leads to marginal flash
flooding concerns along the immediate WA/OR coasts, the terrain of
the Olympics and along the foothills of the Cascades where the
orographic enhancement pattern is defined. PWAT anomalies between
1-1.5 deviations above normal will enter the region by the second
half of the period with the heaviest precip likely coinciding with
the initial moisture surge into the coastal plain. Some modest
instability will be focused along the immediate coast as defined by
the some of the hi- res guidance and mean SBCAPE output within the
ensemble blend. Rates will be generally ~0.5"/hr within the
heavier bands, but some 0.75-1.25"/hr rates are plausible within
the Olympics in Northwest WA state, as well the immediate coast of
WA down into Northwest OR. This is the primary axis of the IVT
pulse with a distinct west to southwest orientation of the mean
flow. This initial surge will be more of a primer for the following
day as the pattern spills into Wednesday, but some isolated flash
flood concerns are plausible within the initial surge of the AR.
The previously inherited MRGL risk was maintained with only a minor
adjustment a touch further south in Oregon to reflect the latest
trends in the mean QPF depicting >2" along the OR coast. Totals
will be generally between 1-3" with isolated to 4" into the Olympic
Peninsula, much of the precip falling within the 00-12z window on
Wednesday.

Kleebauer


Day 3
Valid 12Z Wed Nov 13 2024 - 12Z Thu Nov 14 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS WESTERN
WASHINGTON AND OREGON, NORTHWEST CALIFORNIA, AND OVER THE
SOUTHEASTERN U.S...

...Pacific Northwest...

Atmospheric River from the D2 period continues through much of the
D3 time frame with a waning signal towards Wednesday night into
Thursday. IVT core will come ashore between Astoria down through
the King Range of Southwestern OR with a signal for an additional
2-4" of rainfall with locally as high as 5.5" within the orographic
enhancement in-of the Klamath Mountains. Rates will maintain a
steady- state of 0.25-0.5" over a span of several hours, but the
primary core of the IVT pulse will likely ramp up rates >0.5"/hr
with some 1-1.5"/hr rates plausible across those elevated coastal
areas of OR and Northwestern CA. Rainfall will continue up into WA
state with the heaviest rain confined to the Olympics with an
additional 2-4" likely occurring northwest of Olympia. Two day
totals over the coastal areas of WA/OR will settle between 3-6"
with a max of 8" confined to both the Klamath-Siskiyou and Olympic
Ranges thanks to some orographic enhancement providing localized
QPF maxima that is customary from AR orientations extending from
southwesterly flow.

Additional flash flood opportunities will exist over portions of
Northwest CA to areas south of Mount Shasta where remnant burn
scars will act as an area of heightened concern with local FFG
indices much lower than surrounding areas. Totals will be between
2-4" in this area with the max of 5" occurring over the Northwest
tip of CA north of Eureka where heavier rainfall longevity will
enhance totals locally. A MRGL risk was maintained for the threat
with much of Western WA/OR encompassed, as well as Northwest CA
with an extension inland to south of Mount Shasta to cover for the
burn scar areas that could see >1.5" of rainfall on Wednesday.

...Southeast U.S...

A sprawling surface ridge east of the Mississippi will quickly
migrate eastward allowing for a strong return flow pattern across
the Southeastern U.S along the the western flank of the ridge.
Lingering moisture stemming from the remnants of Rafael will
fester in the Northern Gulf before being ushered poleward around
that clockwise circulation from the high pressure controlling the
pattern across the Mississippi Valley and points east. PWATs will
elevate up close to +2 deviations lending credence to a suitable
airmass for maintaining convective activity. Further west, a
shortwave trough will migrate into the Central Plains with surface
low pressure forming downstream across the Southern Plains/Mid-
Mississippi Valley creating a strengthening convergence pattern
along a cold front that develop on the tail end of the low.
Progressive flow within the setup will alleviate some of the
concerns of lingering precip that will develop from the Lower
Mississippi Valley to points north and east.

The jury is still out on the expected intensity of the precip that
develops, but considering the convective prospects given the
theta-E advection pattern anticipated along with a source of
surface based convergence along and ahead of the forecasted cold
front, some stronger cores capable of rates >1-2"/hr and totals
breaching 3" will be possible, as noted by some of the current
deterministic. Ensemble bias corrected QPF output indicates some
2-3" amounts across parts of the Deep South signaling the threat.
UFVS First Guess Field has a MRGL risk encompassing parts of LA and
MS where the heavy rainfall from recent days has really dropped the
FFG indices across parts of the area. The antecedent conditions
over Southwest and Central LA will be privy to a heightened flash
flood threat leading a MRGL risk extending back into those areas.
The MRGL encompasses much of the Lower Mississippi Valley over into
AL extending up into TN, coinciding with the forecasted meridional
extent of the theta-E progression which would lead to convective
precipitation modes. Will assess as we get closer, but this is the
proxy for where the expected heavier rainfall threats could occur.

Kleebauer

$$
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FOUS30 KWBC 120751
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
251 AM EST Tue Nov 12 2024

Day 1
Valid 12Z Tue Nov 12 2024 - 12Z Wed Nov 13 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS WESTERN
WASHINGTON AND NORTHWEST OREGON...

The previous forecast remains steadfast with the expected totals
and evolution of our next disturbance progged to enter the PAC
Northwest. The next Atmospheric River is currently maneuvering
through the Northeast Pacific with a well-defined IVT pulse located
around the base of a strong, closed upper low and associated
surface cyclone churning over the North Pacific as indicated via
the latest CIMSS MIMIC-TPW satellite derived product. PWAT
anomalies between 1-1.5 deviations above normal will enter the
region by the second half of the period with the heaviest precip
likely coinciding with the initial moisture surge into the coastal
plain, forecast between 21-03z Wednesday (Late-afternoon and early
evening PST). Some modest instability will be focused along the
immediate coast as defined by the hi- res guidance and mean SBCAPE
output within the ensemble blend (HREF/NBM). Rates will be
generally ~0.5"/hr within the heavier bands, but some 0.75-1.25"/hr
rates are plausible within the Olympics in Northwest WA state, as
well the immediate coast of WA down into Northwest OR. This is the
primary axis of the IVT pulse with a distinct west to southwest
orientation of the mean flow. This initial surge will be more of a
primer for the following day as the pattern spills beyond Wednesday
morning, but some isolated flash flood concerns are plausible
within the initial surge of the AR. The previously inherited MRGL
risk was maintained coinciding with the higher (>50%) 12-hr
probabilities of exceeding 2". Totals will be generally between
1-3" with isolated to 5" into the Olympic Peninsula.

Kleebauer


Day 2
Valid 12Z Wed Nov 13 2024 - 12Z Thu Nov 14 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS WESTERN
WASHINGTON AND OREGON, NORTHWEST CALIFORNIA, AS WELL AS PORTIONS OF THE SOUTHEAST AND OHIO VALLEY ...

...Pacific Northwest...

Minimal changes were necessary from the previous forecast issuance
as guidance maintains relevant continuity. Atmospheric River from
the D1 period continues through much of the D2 time frame with a
waning signal towards Wednesday night into Thursday. IVT core will
come ashore between Astoria down through the King Range of
Northwest CA with a signal for an additional 2-4" of rainfall with
locally as high as 5.5" within the orographic enhancement in- of
the Klamath Mountains. Rates will maintain a steady- state of
0.25-0.5" over a span of several hours, but the primary core of the
IVT pulse will likely ramp up rates >0.5"/hr with some 1-1.5"/hr
rates plausible across those elevated coastal areas of OR and
Northwestern CA. Rainfall will continue up into WA state with the
heaviest rain confined to the Olympics with an additional 3-5"
likely occurring northwest of Olympia. Multi-day totals over the
coastal areas of WA/OR will settle between 3-6" with a max of 8"
confined to both the Klamath- Siskiyou and Olympic Ranges thanks to
some orographic enhancement providing localized QPF maxima that is
customary from AR orientations extending from southwesterly flow.

Additional flash flood opportunities will exist over portions of
Northwest CA to areas south of Mount Shasta where remnant burn
scars will act as an area of heightened concern with local FFG
indices much lower than surrounding areas. Totals will be between
2-4" in this area with the max of 5" occurring over the Northwest
tip of CA north of Eureka where heavier rainfall longevity will
enhance totals locally. A MRGL risk was maintained for the threat
with much of Western WA/OR encompassed, as well as Northwest CA
with an extension inland to south of Mount Shasta to cover for the
burn scar areas that could see >1.5" of rainfall on Wednesday.

...Southeast U.S and Ohio Valley...

A sprawling surface ridge east of the Mississippi will quickly
migrate eastward allowing for a strong return flow pattern across
the Southeastern U.S along the the western flank of the ridge.
Lingering moisture stemming from the remnants of Rafael will
fester in the Northern Gulf before being ushered poleward around
that clockwise circulation from the high pressure controlling the
pattern across the Mississippi Valley and points east. PWATs will
elevate up close to +2 deviations lending credence to a suitable
airmass for maintaining convective activity. Further west, a
shortwave trough will migrate into the Central Plains with surface
low pressure forming downstream across the Southern Plains/Mid-
Mississippi Valley creating a strengthening convergence pattern
along a cold front that develop on the tail end of the low.
Progressive flow within the setup will alleviate some of the
concerns of lingering precip that will develop from the Lower
Mississippi Valley to points north and east.

There has been a growing consensus on the expansion of convective
activity across the Deep South into the Ohio Valley with a
formidable heavy rain signature located across the Gulf coast where
the best instability footprint is located, and across the Southern
Ohio Valley where ascent will be maximized within the diffluent
area of the upstream shortwave trough in tandem with the
approaching cold front. QPF off the recent 00z HREF blended mean
in the final 12-hrs signifies some potential for significant totals

2" with a few CAMs depicting as much as 6" across portions of LA

and MS with more of a 2-4" plateau across the Ohio Valley. Ensemble
means are generally stable at 1-2" across a large area, but might
be smoothing out the higher totals as is the bias of the ensemble
blend. In any case, the pattern is certainly favorable for at least
isolated prospects for flash flooding, especially in South-Central
LA where recent QPE from 48 hrs prior sat at 5-10" with locally
higher, so the threat in this locale is greatly enhanced just due
to the antecedent soil moisture anomalies within the past few days.
Further north is not nearly as robust in the soil moisture
anomalies, however some areas within TN and Western KY do have
some lingering top-layer soil moisture from the same event that
occurred in LA. The previous MRGL risk was maintained with a minor
adjustment north into Southern IN as reflected within the latest
QPF trends and expected northern edge of the heaviest precip
Wednesday night into Thursday. Discrepancy in the exact placement
of heavier convection across the Gulf states deterred an additional
upgrade over the region, however the threat for at least one risk
category higher is in play as we move closer to the event. For now,
a blanket MRGL risk was sufficient with the potential for an
upgrade plausible in the next few forecast updates.

Kleebauer


Day 3
Valid 12Z Thu Nov 14 2024 - 12Z Fri Nov 15 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Kleebauer

$$
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FOUS30 KWBC 130749
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
249 AM EST Wed Nov 13 2024

Day 1
Valid 12Z Wed Nov 13 2024 - 12Z Thu Nov 14 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE DEEP SOUTH...

...Southeast U.S and Ohio Valley...

A 1034mb surface ridge is currently analyzed over the Great Lakes
and adjacent Ontario Province with an expected translation eastward
over the next 24 hrs leading to an increasing return flow pattern
over the Southeastern U.S. Current v-vector anomalies pinpoint the
strongest return flow between sfc-850mb bisecting areas from LA
into MS and Western AL leading to ample moisture being pulled
poleward as far north as the Great Lakes. PWAT anomalies on the
order of +2 to +3 deviations will be co-located with the strongest
v-vector component leading to a broadening area of elevated
moisture and accompanying theta-E's indicative of greater
instability, especially the closer you are to the Gulf. Across the
Plains, a potent shortwave trough will shift eastward with
increasing mid and upper level ascent across areas downstream
within the Low to Mid-Mississippi Valley area. The combination of
the pattern evolution will aid in increased convective development
and coverage, especially as we work through the late-morning time
frame and beyond during the period.

Heavy rain potential will be on the rise with the introduction of
the thunderstorm risk with rainfall totals from the latest HREF
blended mean now sufficiently into the 1.5"+ territory with
associated CAMs signaling isolated totals >4" during the time frame
of convective impact. This has ramped up probabilistic signals with
the neighborhood probs now upwards of 40-70% across portions of
South-Central LA through much of MS with the highest probs located
over the MS Delta over to Jackson. Organized convective pattern is
most likely to occur over this area thanks to the approach of a
cold front upstream stemming from surface low development over the
Southern Plains, moving northeast through the Mississippi Valley
after nightfall. Hourly rates within the heaviest convection across
the Deep South is likely to range from 1-2"/hr on average, but some
non-zero prospects for 2.5-3"/hr persists within the CAMs and
expressed through the probability fields on the 00z HREF output.
Typically these signals would warrant a MRGL risk for excessive
rainfall, but considering the soils across parts of LA and MS still
recovering from the onslaught of heavy precip from a few days
prior, the antecedent environment is a bit more conducive for flash
flood prospects. In coordination with the local WFOs within LA and
MS, a Slight Risk was added to encompass areas where heavier
convection is most likely considering the pattern evolution, as
well as covering the areas where top layer soil moisture anomalies
lie above the 70th percentile as reported by the updated NASA SPoRT
data.

The remainder of the Southeast and points up into the Ohio Valley
will maintain the previous MRGL risk forecast with only a minor
expansion to the north and east to account for some of the trends
of increasing heavy rainfall potential through Northern KY as the
system remains fairly progressive in its forward propagation.
Limited instability will also cap the risk for significant rainfall
rates, but instances of >1"/hr are certainly plausible considering
the prime mid-level evolution and approaching cold front providing
surface based forcing. Totals will be closer to the 1-2" range for
most, but 2-3" is within reason in the heaviest rain cores.

...Pacific Northwest...

Atmospheric River from this evening will continue to unfold across
the Pacific Northwest with the IVT pulse orienting further south
through the morning and early afternoon with heavy rain impacting
areas of Southwest OR through much of Northwestern CA with the
heaviest rain focused at the immediate coast into the interior
terrain aligning from the Klamath Mountains down towards the King
Range south of Eureka. The forecast has been very consistent on the
threat the past several days with little deviation in the expected
outcome with totals ranging from 2-4" at the immediate coast from
WA down through Northern CA with 3-6", local maxima of 8" during
the 48-hr period of impact over places like the Olympic Range in WA
state and the Klamath Range down in Southwestern OR. The premise of
the MRGL risk was mainly for 3 or 6 hour FFG exceedance intervals,
along with some 24 hour FFG potential, mainly located over the
Olympics for the latter index. Hourly rates will be majority sub-
FFG exceedance, however some 1-1.5"/hr rates during the height of
the IVT surge Wednesday morning over the coastal mountain ranges
could be sufficient for isolated flooding prospects before becoming
more of an accumulative rainfall concern over time. The one area
where the heavier precip is not anticipated but still a relative
concern remains in the area located south of Mount Shasta and
points west where remnant burn scars maintain locally lower FFG
indices leading to a heightened threat for flash flooding where the
scarring is located. This is the reason for the inland extent
across Northern CA and to maintain consistent messaging with the
local WFO for the threat.

Kleebauer


Day 2
Valid 12Z Thu Nov 14 2024 - 12Z Fri Nov 15 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Kleebauer


Day 3
Valid 12Z Fri Nov 15 2024 - 12Z Sat Nov 16 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Kleebauer

$$
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FOUS30 KWBC 140754
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
254 AM EST Thu Nov 14 2024

Day 1
Valid 12Z Thu Nov 14 2024 - 12Z Fri Nov 15 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Maturing surface cyclone off the VA/NC coast will amplify
rainfall prospects over the VA Tidewater into Eastern NC late this
afternoon and evening with a developing axis of deformation driving
elevated convective concerns in the aforementioned areas. Totals
between 1.5-3" are forecast within these zones with some minor
flooding possible over urban zones and the immediate coast,
coinciding with coastal flooding likely occurring. Rainfall rates
will fall short of the necessary criteria to meet FFG exceedance,
however a non-zero threat will exist for flash flood concerns
across Northern NC into Southern and Southeast VA in urban zones
that are more prone to flooding prospects. This is still below the
5% threshold necessary for flash flooding leading to a continued
nil ERO, but non-zero threat.

Kleebauer


Day 2
Valid 12Z Fri Nov 15 2024 - 12Z Sat Nov 16 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Kleebauer


Day 3
Valid 12Z Sat Nov 16 2024 - 12Z Sun Nov 17 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Kleebauer

$$
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FOUS30 KWBC 180833
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
433 AM EDT Fri Oct 18 2024

Day 1
Valid 12Z Fri Oct 18 2024 - 12Z Sat Oct 19 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE SOUTHERN INTERMOUNTAIN REGION AND ADJACENT SOUTHERN HIGH PLAINS...

Overall...the synoptic pattern continued to maintain good
continuity with previous runs...showing ab upper trough/closed-
low over the Great Basin that eases eastward with time and the
strongest large scale ascent maximized downstream of the mean
trough with a pronounced diffluent pattern. This has allowed the
the Day 2 outlook from Thursday to propagate into the Day 1 outlook
without significant change. Ensemble guidance is in
relative agreement on the placement of two maxima during the
forecast period; one located Northeast AZ into Southeast UT with
the initial diffluent signature ahead of the evolving upper low
over the Great Basin, and the secondary maxima across Northeastern
NM where the convergence pattern aided by increasing large scale
ascent will generate a period of heavier precip this evening and
into the early morning hours of Saturday morning. Did make a minor
adjustment in moving the Marginal risk area around most of the
Sangre de Cristo area to avoid too much overlap with the WPC winter
weather desk deterministic snowfall forecast. Slot canyons, and
flashier river basins within the Four Corners area will offer a
greater risk of flash flooding with a secondary threat over the
remnant burn scars in northern New Mexico, This allowed for a
maintenance of the previous MRGL risk.

Bann


Day 2
Valid 12Z Sat Oct 19 2024 - 12Z Sun Oct 20 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE SOUTHERN HIGH PLAINS INTO SOUTHEAST COLORADO...

...Southern Plains...

Forecast rainfall continues to slowly increase across the southern
Plains in response to a quasi-stationary stationary upper low which
begins to tap deeper moisture will begin to tap into increasing
Gulf moisture. By Day 2/Friday the moisture plume will be well
established. Given the steering flow changes will be slow, the
excellent forcing east of the upper level low and increasing
instability will all favor the development of storms on Saturday capable
of producing heavy downpours that lead to flooding/flash flooding
over an otherwise mostly parched/arid area. While individual storms
may be progressive given the low level wind speeds involved, the
placement of the strongest forcing moves little on
Saturday/Saturday night suggesting the threat of repeat convection
or training of cells...especially over northeast New Mexico.
Modified the previous Marginal risk area to avoid the highest
terrain of the Sangre de Cristo range given the elevation forcing
the predominant precipitation type as snow.

...Northwestern Washington State...

As the Day 3 period begins at 12Z on Saturday...a well defined
atmospheric river should be settling into Washington from the
north, resulting in local rainfall totals of 3-5 inches for the
period. Integrated Vapor Transport values at the peak could exceed
900 kg/m/s, which is a bit stronger than the typical A.R., but
nothing major. When added to Friday's rain totals, this will likely
be enough rain to result in isolated flash flooding. Even if the
highest elevations see snow, the large majority of the rainfall
into the mountains will be in the form of rain. Saw little reason
to make to many changes to the region of greatest excessive risk
based on terrain- forced upslope/downslope regions at this point.
Only the first 12 hours of the Day 2 period were covered by the
18/00Z HREF probabilities...but the probabilities of 2 inch amount
of liquid precipitation are roughly 50 percent in the terrain of
the Olympics and the far northern Cascades.

Bann


Day 3
Valid 12Z Sun Oct 20 2024 - 12Z Mon Oct 21 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE SOUTHERN AND CENTRAL HIGH PLAINS...

There threat of excessive rainfall is expected to linger into
Sunday from parts of northeast New Mexico and adjacent portions of
the Texas panhandle northeastward into southwest Kansas in a region
of upper level difluence east of the closed low/upper trough
back closer to the four-corners region. The additional rainfall in
this period does not look to be blockbuster in nature...perhaps 1
to 1.5 inches...but it will be in addition to the amounts that fall
mainly in the Day 2 period. During the period... model guidance
suggests a weakening of the upper level feature near the four-
corners and surface high pressure building southward east of the
front range will help lead to decreasing coverage and rainfall
intensity with time.

Bann
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FOUS30 KWBC 160802
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
402 AM EDT Wed Oct 16 2024

Day 1
Valid 12Z Wed Oct 16 2024 - 12Z Thu Oct 17 2024

The probability of rainfall exceeding flash flood guidance is less than
5 percent.

Kleebauer


Day 2
Valid 12Z Thu Oct 17 2024 - 12Z Fri Oct 18 2024

...2030Z Update...

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Kleebauer


Day 3
Valid 12Z Fri Oct 18 2024 - 12Z Sat Oct 19 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
NORTHERN NEW MEXICO INTO SOUTHERN COLORADO...

Longwave pattern will evolve into a fairly prolific upper
trough/closed-low over the Great Basin, slowly migrating eastward
with sights on the Four Corners. Large scale ascent will become
maximized downstream of the mean trough with a pronounced diffluent
pattern in-of the Southern Rockies, including the Sangre de Cristo
and San Juan mountain ranges where heavier precip is forecast. A
cold front will slowly propagate eastward from the primary
disturbance with a return flow setup pressing westward across the
Eastern NM plains on the western flank of a sprawling surface high
east of the Mississippi. A secondary cold front to the north will
plunge southward thanks to a strong ridge of high pressure
developing upstream in wake of the primary western low, along with
a lee side trough developing over the Front Range. The tandem of
boundaries and backed flow will converge over Northern NM with a
strong isentropic ascent pattern initiating later Friday evening
through Saturday AM and beyond.

Convective signals are most pronounced in the initial stages of
the pattern evolution mainly due to the return flow setup where
more unstable air will advect northwestward into the Eastern NM
plains before banking against the lee of the Southern Rockies. Both
ensemble and deterministic output for heavy precip are locked in
across the area encompassing much of Northern NM, but especially
within the confines of places like Raton and points south where
topographic enhancement within the convergent axis will generate
local precip maxima when the convergence pattern truly solidifies
late in the period. Totals of 1-2" of precip are forecast on the
southern edge of the San Juans down into portions of the Sangre de
Cristos, closing in on some of the prevalent burn scars in the
region. A secondary maxima of 1-2" is forecast over that main axis
of convergence over Northeastern NM in vicinity of the eastern
flank of the Sangre de Cristos, including places like Taos and
Angel Fire over into parts of the plains in the lee of the mountain
chain. The period before will be more of a primer for the main
event this period through the following D4 time frame. The
combination of better moisture return and large scale forcing via
diffluent mid- level flow and jet coupling provides ample support
for a continuation of the previous MRGL risk, as well as an
expansion of the risk area further southwest and east to match the
ensemble QPF footprint in areas of highest convective potential.

Kleebauer
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FOUS30 KWBC 170804
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
404 AM EDT Thu Oct 17 2024

Day 1
Valid 12Z Thu Oct 17 2024 - 12Z Fri Oct 18 2024

Relative progressive nature of precipitation across Northern NM
will alleviate much of the flash flood concerns this afternoon,
however the very low FFG's in place over each existing burn scar
within the Sangre de Cristos will offer an opportunity for
localized flooding within each impacted zone. Current HREF probs
for >1" of precip is around 50-60% within the neighborhood derived
analysis. This is still very lacking within the EAS prob field
leading to a pattern of less widespread heavier precipitation
totals and more relegated to very localized maxima likely over the
tops of the mountain chain. The best depiction is outlined over the
San Juan Mountains where a majority of the precipitation will fall
as snow or a rain/snow mix mitigating the threat for flash flooding
during the period. This has allowed for a continuation of the nil
ERO across the CONUS, but still a non-zero presence within the burn
scars of Northern NM.

The probability of rainfall exceeding flash flood guidance is less than
5 percent.

Kleebauer


Day 2
Valid 12Z Fri Oct 18 2024 - 12Z Sat Oct 19 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE FOUR CORNERS REGION THROUGH NORTHERN NEW MEXICO...

Longwave pattern will continue evolving into a fairly prolific
upper trough/closed-low over the Great Basin, slowly migrating
eastward with sights on the Four Corners. Large scale ascent will
become maximized downstream of the mean trough with a pronounced
diffluent pattern in-of the Southern Rockies, including the Sangre
de Cristo and San Juan mountain ranges where heavier precip is
forecast. A cold front will slowly propagate eastward from the
primary disturbance with a return flow setup pressing westward
across the Eastern NM plains on the western flank of a sprawling
surface high east of the Mississippi. A secondary cold front to the
north will plunge southward thanks to a strong ridge of high
pressure developing upstream in wake of the primary western low,
along with a lee side trough developing over the Front Range. The
tandem of boundaries and backed flow will converge over Northern NM
with a strong isentropic ascent pattern initiating later Friday
evening through Saturday AM and beyond.

There has been very little deviation in the guidance to amass much
of a change compared to the previous forecast, so a general
continuity was maintained from the inherited MRGL risk across the
Four Corners into Northern NM. Ensemble guidance is in relative
agreement on the placement of two maxima during the forecast
period; one located Northeast AZ into Southeast UT with the initial
diffluent signature ahead of the evolving upper low over the Great
Basin, and the secondary maxima across Northeastern NM where the
convergence pattern aided by increasing large scale ascent will
generate a period of heavier precip Friday evening into Saturday
morning and beyond. Each areal maxima is similar with regards to
precip magnitude with a general neighborhood 1-2" max with a small
chance at upwards of 2.5" across the western maxima within the best
upper ascent within the nose of the 100kt 250mb jet streak. The
secondary maxima is generally within the last 12-hr window
encompassing 00-12z Saturday with the heaviest QPF footprint
actually highest in D3 (More on that in the D3 period below). In
any case, the very dry antecedent conditions, slot canyons, and
flashier river basins within the Four Corners area will offer a
greater risk of flash flooding with a secondary threat over the
remnant burn scars in Northern NM. This allowed for a maintenance
of the previous MRGL risk.

Kleebauer


Day 3
Valid 12Z Sat Oct 19 2024 - 12Z Sun Oct 20 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS
OF THE SOUTHERN HIGH PLAINS INTO SOUTHEASTERN COLORADO...

Closed upper circulation will slowly migrate eastward with a
persistent diffluent channel focused in-of the Eastern NM High
Plains up into the Colorado Front Range for Saturday. A uni-
directional flow located within the lowest 600mb will persistent
through much, if not all the forecast period allowing for moist
unstable air to be pulled poleward into the confines of the Caprock
and points north. ECENS PWAT anomalies are forecast to run upwards
of 3-3.5 deviations above normal with an M-Climate Percentile
(Forecasts relative to the last 20 years during time of year) that
is peeking into the seasonal max, a testament to the anomalous
nature of the moisture advection regime. With the poleward
advancement of the airmass, regional theta-E's spike with a theta-E
ridge positioning located right over the NM/TX border running clear
into Front Range of CO and nearby KS. This signal is consistent
with a persistent band of rainfall likely to be situated within the
theta-E ridge mentioned above and just out ahead of the slow-moving quasi-stationary front trailing the very slow moving to perhaps stationary
low pressure across Southern CO.

Precip totals of 2-4" with locally higher amounts are increasingly
likely within that corridor between Clovis up through Southeastern
CO with the max likely driven by repeating convection as small
mid-level perturbations rotate around the general upper circulation
and move overhead of the areas above. The only saving grace for a
more significant flash flood potential is the antecedent conditions
leading in are very dry with the 0-10cm relative soil moisture
percentiles running between 5-20% across the area anticipated to
see the most rainfall. Initial rains will be beneficial, but will
add through the course of the period with waves of heavier rain
likely exacerbating areas by later in the period into early Sunday.
The previous SLGT risk was generally maintained with a MRGL
surrounding. Both risks were expanded somewhat on the southern and
northern peripheries to account for a trend in an expansion of
precip latitudinally in either direction. The heaviest will likely
encompass Eastern NM into Southeast CO with these areas likely
trending towards the higher end of SLGT risk if the signal remains
and/or amplifies further.

Kleebauer
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FOUS30 KWBC 130801
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
401 AM EDT Sun Oct 13 2024

Day 1
Valid 12Z Sun Oct 13 2024 - 12Z Mon Oct 14 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE UPPER FLORIDA KEYS INTO THE SOUTHEAST FLORIDA URBAN CORRIDOR...

No changes were made to the inherited Marginal risk area over the
southeast FL urban corridor. Isolated convection will be ongoing at
12z this morning along the coastal convergence axis...with another
round of activity likely this afternoon. It is the afternoon
convection that appears to have better instability to work with,
and thus a better chance of more robust development. Coverage
remains a question, but high res guidance suggests a weak surface
trough/wave moving across south FL should help locally enhance
convergence this afternoon.

With any deeper convection tapping into the stronger westerly flow
aloft, the tendency may be for cells to have more of an eastward
motion this afternoon, limiting rainfall duration as cells move
offshore. However if low level easterly flow is strong enough
and/or the low level convergence axis is persistent enough, then
we could see at least some cell training for a period of time.
Overall the ingredients are in place to suggest a localized flash
flood risk is a possibility. HREF guidance supports isolated 3"
totals, but there is minimal model support for amounts much higher
than that. The Marginal risk should cover this isolated urban
flash flood threat...as not seeing enough support for Slight risk
level impacts/coverage at this time.

Chenard


Day 2
Valid 12Z Mon Oct 14 2024 - 12Z Tue Oct 15 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Chenard


Day 3
Valid 12Z Tue Oct 15 2024 - 12Z Wed Oct 16 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Chenard
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FOUS30 KWBC 110721
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
321 AM EDT Fri Oct 11 2024

Day 1
Valid 12Z Fri Oct 11 2024 - 12Z Sat Oct 12 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Easterly low level flow will bring showery conditions to the
central and southeast Atlantic coast of FL today into tonight.
However with PWs below 2" and instability limited not currently
expecting rainfall rates or totals to reach levels of concern for
flash flooding. Thus we will continue to carry no risk area in the
ERO.

Chenard


Day 2
Valid 12Z Sat Oct 12 2024 - 12Z Sun Oct 13 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE UPPER FLORIDA KEYS INTO THE SOUTHEAST FLORIDA URBAN CORRIDOR...

Moisture and instability return northward into southern FL Saturday
into Saturday night, with PWs increasing towards 2.25" and CAPE
over 1000 j/kg. Meanwhile a weak wave moving into the eastern Gulf
of Mexico may result in an uptick in low level flow and
convergence. Thus expect we should gradually see an uptick in
convective coverage this weekend over the Keys into south FL.

Easterly low level flow and westerly upper level winds support the
potential for slow moving convective cells near the coastal
convergence axis. Timing remains a bit uncertain, and the better
convective coverage may end up more over the Keys this period
(where flash flooding is harder to come by), but given the
increasing moisture and instability there is at least a conditional
threat of localized flash flooding Saturday into Saturday night
into the more urban areas of southeast FL. If deep convection does
indeed develop then urban flash flooding is possible from the
upper Keys into southeast FL.

Chenard


Day 3
Valid 12Z Sun Oct 13 2024 - 12Z Mon Oct 14 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE UPPER FLORIDA KEYS INTO THE SOUTHEAST FLORIDA URBAN CORRIDOR...

The risk on day 3 is a continuation of the threat on day 2 over
Southeast FL. The overall thermodynamic ingredients remain the
same, however there is a chance that forcing will be stronger by
Sunday. Still some timing and positional differences amongst the
guidance, but the general consensus is for a weak wave to move
across FL Sunday, which should both result in a subtle uptick in
mid/upper forcing and locally enhance lower level convergence.

Thus currently expecting a greater chance of loosely organized
convective clusters Sunday into Sunday night...and with wind fields
still supporting slow moving cells...this activity could tend to
anchor along the coastal convergence axis for a while. Thus
isolated urban flash flooding is considered possible. Certainly a
chance that a Slight risk may be needed for one of these weekend
days...but given some uncertainty with the synoptic evolution and
convective coverage, think a good first step is just introducing
Marginal risks for both days 2 and 3 (Sat and Sun) and continue to
monitor trends.

Chenard
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FOUS30 KWBC 120752
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
352 AM EDT Sat Oct 12 2024

Day 1
Valid 12Z Sat Oct 12 2024 - 12Z Sun Oct 13 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE UPPER FLORIDA KEYS INTO THE SOUTHEAST FLORIDA URBAN CORRIDOR...

Moisture and instability return northward into southern Florida
today which should result in deeper convection and the potential
for higher rainfall rates with PWs increasing towards 2.25".
Meanwhile a weak wave moving into the eastern Gulf of Mexico should
result in an uptick in low level flow and convergence. Thus expect
we should gradually see an uptick in deeper convective coverage
over the Keys into south FL and the adjacent waters today into
tonight.

The overall synoptic pattern still looks to favor slow moving
convective cells along and near the coastal convergence axis given
easterly low level flow and westerly upper level winds. Timing and
the CAPE distribution over land remain a bit uncertain. Some model
guidance wants to keep the better instability and convergence
offshore or over the Keys, while others shift these ingredients
more into the Southeast Fl coastal urban corridor. This decreases
confidence with regards to convective evolution.

The ingredients in place in the vicinity certainly support the
potential for a localized higher end flash flood event somewhere
within the southeast FL urban corridor today and/or tonight.
However the signal in the 00z HREF guidance is mixed, and overall
just not seeing enough in the probability fields to suggest we are
at Slight risk level coverage or confidence at this time. Thus we
will maintain the Marginal risk and continue to monitor
observational and model trends.

Chenard


Day 2
Valid 12Z Sun Oct 13 2024 - 12Z Mon Oct 14 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE UPPER FLORIDA KEYS INTO THE SOUTHEAST FLORIDA URBAN CORRIDOR...

The risk on day 2 is a continuation of the threat on day 1 over
Southeast Florida. The overall thermodynamic ingredients remain
similar, however there is still spread with the mesoscale to
synoptic setup. The 00z GFS and ECMWF have trended quicker with the
weak wave and suggest the better organized convective risk Sunday
will now be offshore and over the Bahamas. However the Gem Reg and
some HREF members appear slower and focus more convection over
south FL.

The uncertainty in these details appears too large to go with
anything more than a Marginal risk at this time. Overall do tend to
think the flood risk Sunday is trending down compared to what it
looked like last night (given the trends noted in the ECMWF and
GFS), but favorable moisture and instability parameters suggest at
least a localized flash flood risk could persist.

Chenard


Day 3
Valid 12Z Mon Oct 14 2024 - 12Z Tue Oct 15 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Chenard
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FOUS30 KWBC 100827
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
427 AM EDT Thu Oct 10 2024

Day 1
Valid 12Z Thu Oct 10 2024 - 12Z Fri Oct 11 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
EAST-CENTRAL TO NORTHEAST FLORIDA...

Heavy rainfall from Milton continues to quickly move east across
the Florida Peninsula. Additional rain of 1 to 4 inches is likely
over the next couple hours along portions of the central and
northern FL east coast. However based on recent radar and HRRR
trends it appears likely that most, if not all, of this heavier
rain will be offshore by 12z this morning. Thus while areas of
considerable flash flooding will continue over the next few hours,
the expectation is that additional flash flooding after 12z will be
minimal. For that reason we will carry only a Marginal risk on the
new day 1 ERO that goes into effect at 12z this morning. The
ongoing High risk remains valid for the next couple hours until
12z. Keep in mind that even after the heavy rain ends, significant
areal and river flooding will continue to be a concern in areas
that have received significant rainfall.

Chenard


Day 2
Valid 12Z Fri Oct 11 2024 - 12Z Sat Oct 12 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Chenard


Day 3
Valid 12Z Sat Oct 12 2024 - 12Z Sun Oct 13 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Chenard

d
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FOUS30 KWBC 080816
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
416 AM EDT Tue Oct 8 2024

Day 1
Valid 12Z Tue Oct 08 2024 - 12Z Wed Oct 09 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR MUCH OF THE
FLORIDA PENINSULA...

No significant changes were made to the ERO risk areas for this period.

"The calm before the storm" will be in place over much of Florida
today. This isn't to say it won't rain anywhere...but the risk of
heavy rain causing flooding on most of the Peninsula today will
most certainly be the lowest of the next few days. A stationary
front in the same tropical moisture plume as Milton is draped
across southern Florida. This is providing a focus for heavier
showers and storms south of the front from Miami south through the
Keys. Since the storms are tracking parallel to the front, training
is a significant concern this morning. As any mesolow tracking
along the front moves off, the heavy rain threat in the Keys should
diminish by this afternoon due to increasing influence of Milton.
For the rest of the Florida Peninsula, most of today should be dry,
especially the further north you go. This is because drier air
associated with a jet across the Panhandle is sinking southward
with a front and will ultimately catch Milton and force
extratropical transition as it approaches Florida. For today
however, it will keep things largely dry along and north of the
eventual track of the storm.

The rainfall threat (and the basis for the ongoing Slight) is
largely tied to any showers and storms that may form...most likely
from mesoscale effects like differential heating and sea breezes.
Due to an excess of atmospheric moisture over most of Florida with
PWATs of 2.25 to 2.75 inches today, any storms that form, even if
disorganized and not associated with any discernible forcing...will
have a superabundance of moisture to work with to convert to
rainfall. Much of south Florida has seen multiple inches of rain
over the past few days. While not prolific enough to cause
widespread flooding concerns, they have kept soils close to
saturated. This will play a role in the eventual flooding concerns
with Milton. 00Z HREF guidance highlights portions of the Treasure
Coast with the highest chances of 3 inches or more of rain today
not directly associated with Milton.

A higher end Slight remains in place for the Gulf Coast from Tampa
south through Naples. This is largely tied to the initial rain
bands from Milton which will begin to impact the coast in the
predawn hours Wednesday before the start of the Day 2 period.

Wegman


Day 2
Valid 12Z Wed Oct 09 2024 - 12Z Thu Oct 10 2024

...THERE IS A HIGH RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
CENTRAL FLORIDA...

...WIDESPREAD AND NUMEROUS INSTANCES OF FLASH FLOODING ARE
EXPECTED WITH LIFE-THREATENING AND CATASTROPHIC FLASH FLOODING PROBABLE...

With the ingestion of some of the longer range CAMs into the model
suite, the forecasted rainfall directly associated with Hurricane
Milton's crossing of the Florida Peninsula has increased markedly
from previous forecasts. The latest storm total rainfall has over
11 inches of rain for Tampa, 8 inches near and north of Orlando,
and 5.5 inches for Jacksonville. The corridor of the High risk
following the entire length of I-4 has seen the most impactful
increases in forecasted rainfall. Obviously there has been a nearly
historic increase in Milton's strength in the last 24 hours, and
all of this added energy and Gulf moisture will mean more rainfall
to come along its track, despite its fast forward speed.

The heaviest rainfall amounts along I-4 and north will generally
will be immediately along and north of the most probable track of
Milton's center. As mentioned in the NHC discussions, Milton is
expected to be well into the process of extratropical transition by
the time the storm crosses the Peninsula. This process should
greatly limit the amount of rainfall expected south of the center,
as dry air entrainment into the southwest quadrant of the storm is
an essential aspect of the extratropical transition process. Thus,
nearly all of the impressive tropical moisture associated with
Milton will be focused along and north of the center, and therefore
represents the greatest threats for flash flooding. The ERO risk
categories drop off a bit slower on the south side since the
predecessor rainfall event (PRE) of the past couple days and today
was largely focused on south Florida, as the stationary front that
has been there has persisted. Inflow into Milton's circulation and
the eventual development of a cold front south of the center
should still lead to bands of rain criss-crossing south Florida
from west to east. Since the PRE saturated this area the most...the
lesser amounts of rain expected here may still cause flooding
impacts...so the ERO risk categories south of the track may be a
bit generous.

Meanwhile on the north side of the circulation, abundant dry air
associated with a separate cold front and jet streak over the
Panhandle and far north Florida should act as a very effective sink
for the portion of Milton's rainfall that drifts too far away from
the center. Since this area has been quite dry in recent days, the
threat for flooding will be much more constricted, and therefore
the ERO risk categories are much more compact.

The additional rainfall now in the forecast will be one factor for flooding...while another one will be storm surge and tidal
flooding, especially south of the center where the flow will be
onshore and to a slightly lesser but still impactful extent, to
the north of the center on the Atlantic side where there will also
be onshore flow. At the time of high tide and the storm surge, the
added water from the Gulf/Atlantic will effectively block effective
drainage from the rainfall falling over the interior. The 6-12
inches (with locally higher amounts of rainfall) having nowhere to
drain due to the high tide and storm surge flooding will also work
to exacerbate the flooding impacts from Milton since that rain
water will have nowhere to drain.

Given all of the above, and despite the small to medium size of the
storm and the acceleration of the storm in the forecast, a High
Risk was introduced in coordination with TBW/Tampa, FL;
MLB/Melbourne, FL, and JAX/Jacksonville, FL forecast offices. It's
probable that the greatest flooding impacts will be with storm
surge primarily, but also the portions of the nearshore rivers,
streams, and creeks (especially near landfall) where the inland
flood waters from heavy rainfall are unable to drain to the Gulf.

Wegman


Day 3
Valid 12Z Thu Oct 10 2024 - 12Z Fri Oct 11 2024

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR ORLANDO AND
PORTIONS OF THE FIRST AND SPACE COASTS...

A rare double upgrade was introduced with this update, with
potential for further adjustments with future updates. The latest
guidance suggests that the wraparound rain to the north and
northwest of the center of Milton will persist well into the day on
Thursday. Thus, associated forecast rainfall has increased
markedly from the previous forecasts. For the Moderate Risk area,
expect an additional 2 to 4 inches of rain after the 12Z/8am
Thursday start of the day 3 period. With a High Risk on Day 2,
further increases in the forecast rainfall may require a High Risk
in this general area to continue into Thursday. Obviously,
adjustments in the speed and track of Milton as it races off the
coast will result in additional big changes to this ERO forecast.

Essentially, the Day 3 ERO is just a continuation of the Day 2
rainfall with Milton. The vast majority of the rainfall for the
period will fall during the day Thursday, and expect trimming and
downgrades through the day as the rain ends from west to east.
Expect widespread and catastrophic flooding from the Day 2 period
to continue through the Day 3 period as the rain ends.

Wegman
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FOUS30 KWBC 060758
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
358 AM EDT Sun Oct 6 2024

Day 1
Valid 12Z Sun Oct 06 2024 - 12Z Mon Oct 07 2024

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR THE MIAMI-
FORT LAUDERDALE METRO...

In coordination with the MFL/Miami, FL forecast office, a Moderate
Risk upgrade was introduced with this update.

A weak surface low is developing over the eastern Gulf well east of
T.S. Milton, but in the same plume of incredibly deep tropical
moisture. The low will drift southeastward toward south Florida.
This will increase the easterly flow over the Straits of Florida
between the Bahamas and Florida. This increased easterly flow in an
air mass with PWATs between 2.25 and 2.5 inches will both increase
the concentration and intensity of resultant thunderstorms over the
Gold Coast.

Portions of the Ft. Lauderdale and Miami metros saw up to 3 inches
of rain on Saturday. Rainfall amounts today and especially tonight
may accumulate to over 6 inches in that time. With saturated soils
and urban effects, the threat for ponding and flooding in the area
has greatly increased. Expect numerous areas of ponding and
flooding from today's rainfall, which necessitated the Moderate
Risk upgrade.

Elsewhere, the surrounding Slight Risk was expanded to include the
Gulf Coast from Tampa south and the Atlantic coast from Cape
Canaveral south. The aforementioned low will enhance rainfall rates
along much of the Gulf Coast from Tampa south, where heavy rainfall
Saturday caused localized flash flooding. This additional rainfall
on saturated soils will cause renewed flash flooding, mostly in
urban areas. Further north up the Atlantic coast, similar
convergence as further south is expected, but with lesser forcing,
resulting in lower rainfall amounts for the Treasure and Space
Coasts. Widely scattered instances of flash flooding are expected.

Finally, for the middle of the Florida Peninsula, the area will be
furthest from the strongest forcing, resulting in a local minimum
of rainfall. Since the area will not have tidal flooding concerns
and is somewhat less developed, only isolated flash flooding is
expected. The threat for heavy rainfall will continue up to the
Georgia coast however, where a local convergence zone may develop
as indicated in several of the CAMs. The Marginal was expanded
north to account for this possibility.

Wegman


Day 2
Valid 12Z Mon Oct 07 2024 - 12Z Tue Oct 08 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
SOUTHERN FLORIDA PENINSULA AND THE KEYS...

The weak surface low that will bring heavy rain to south Florida on
Sunday will continue eastward over the Peninsula and into the
Bahamas by Monday afternoon. Heavy rain will likely continue over
the southern Peninsula through at least Monday morning. There is
considerable disagreement on the track, strength and the speed of
the low, which will play a major role in how long the heavy rain
persists into Monday afternoon. With somewhat better agreement that
rainfall amounts will at least be lower than on Sunday, the Slight
risk for the area that was inherited was largely maintained, albeit
including some of the interior of the Peninsula as soils become
saturated area-wide, resulting in close to 100% conversion of heavy
rain to runoff. An internal higher-end Slight is in place for the
Gold Coast, for the potential that should amounts from Sunday
verify, then another targeted Moderate Risk upgrade will be
necessary. Meanwhile, a second day of very heavy rain and
thunderstorms is expected to impact all of the Keys, which at high
tide times may cause flooding due to poor drainage.

With some of the other CAMs moving the low across the southern
Peninsula and east to the Bahamas, portions of the Gulf Coast,
especially north of Ft. Myers/Cape Coral up through Tampa are in
the rare decreasing trend in the forecast rainfall amounts on
Monday. Thus, the Slight that extended up through Tampa was
downgraded to a Marginal north of Ft. Myers/Cape Coral with this
update.

Wegman


Day 3
Valid 12Z Tue Oct 08 2024 - 12Z Wed Oct 09 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR MUCH OF THE
FLORIDA PENINSULA...

The PRE (predecessor rain event) will enter its third and final day
over the Florida Peninsula on Tuesday. The trough that occasionally
spins up weak surface lows will remain in place across the
Peninsula. The circulation of what will then be Hurricane Milton
will make its approach to the Gulf Coast of Florida, likely near
Tampa very late Tuesday night/early Wednesday morning. At this
time, expect little of the rainfall directly associated with
Milton's core to yet impact the Florida Peninsula. Of course, with
future updates and forecast changes from NHC, this may change.
Given the inherent uncertainty with the track and speed of this
small hurricane, the Slight over the Peninsula was maintained,
albeit with some filling in in the middle of the Peninsula near the
Orlando area. There remains a bimodal distribution of the rain with
much more expected along the Gulf coast from Tampa down through
Naples, but with a secondary maximum for the Space and First
Coasts.

With the latest guidance, there is some offset of the axis of
heaviest rainfall ahead of Milton. The northward trend will reduce
amounts in portions of the hard-hit Gold Coast in favor of more
rain for the northern Peninsula towards the First Coast. By Tuesday
the greatest overlap will be over the Gulf Coast. It is here than
an internal higher-end Slight was introduced for the Tampa through
Naples area due to increasing amounts of heavy rain moving into the
coast, being moved along by the predominant southwesterly flow in
the trough ahead of Milton's core circulation. Heavy rainfall both
the past couple days as well as expected both today and Tuesday
should keep all of the soils on the Florida Peninsula at or near
saturation, resulting in nearly all of the rainfall converting to
runoff. Thus, progressively less rainfall will be needed to result
in flooding.

Despite Milton and directly associated rains largely holding to the
Day 4/Wednesday period, it appears that similar to Helene, most of
the rain over the Florida Peninsula will be associated with the
PRE, while the heaviest rain (as well as wind and storm surge) will
conclude the multi-day rain event with Milton moving through,
causing much more widespread flooding.

Wegman
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FOUS30 KWBC 070823
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
423 AM EDT Mon Oct 7 2024

Day 1
Valid 12Z Mon Oct 07 2024 - 12Z Tue Oct 08 2024

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR THE GOLD
COAST AND THE UPPER FLORIDA KEYS...

Very few changes were made to the inherited EROs for this period.

A leading low, front, and surface trough over the eastern Gulf and
Florida well ahead of Hurricane Milton continues to spread rain
over nearly all of the Florida Peninsula this morning. The low will
shift east over the Everglades and South Florida today. Ahead of
the low, additional showers and thunderstorms capable of very heavy
rainfall rates due to the extremely moist environment will
continue. Portions of the Gold Coast saw 2-4 inches of rain
yesterday, resulting in localized flash flooding, so the potential
for that much rain again today supports the continuance of the
Moderate Risk. The trailing front south and west of the low will
remain stationary near Southwest Florida and the Keys. This will
keep the threat for heavy rainfall ongoing through tonight. The
Slight Risk area remains in place for these regions as far
southwest Florida is the swampy Everglades and the Keys present
very small targets for heavy rain. If training cells were to move
over the Keys during high tide then flooding is probable.

HREF probabilities suggest the heaviest rain today all over south
Florida are more likely to remain offshore, so the heavy rain
threat is slightly lower today compared to yesterday/Sunday.
Convergence along the Atlantic coast remains prevalent today, so
the Slight Risk remains in place to the north through the Space and
Treasure Coasts. With the center of the low tracking over south
Florida and off to the east towards the Bahamas, this should give
the likely landfall areas of the Gulf Coast north of Ft. Myers
through Tampa a general reprieve from heavy rain for most of today.

Wegman


Day 2
Valid 12Z Tue Oct 08 2024 - 12Z Wed Oct 09 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR MUCH OF THE
FLORIDA PENINSULA...

There will be a general lull in the overall general rainfall across
Florida on Tuesday. The "calm before the storm". The low impacting
most of the state Monday will be well east of the Bahamas by
Tuesday, while the rainfall directly associated with Hurricane
Milton will likely remain off or just arriving at the Gulf Coast
before 12Z Wednesday. Nevertheless, widespread light to moderate
rainfall will impact the state Tuesday and Tuesday night. Thus, any
resultant flooding will be largely due to favorable antecedent
conditions due to generally widespread saturated soils across the
Peninsula. Further, continued extremely moist atmospheric
conditions consistent with the deep tropical air mass with PWATs
around 2.25 inches will still support locally heavy rainfall with
any convection that manages to form.

On the Atlantic side, a convergence zone may remain over the Space
and Treasure Coasts on Tuesday, which could locally organize any
convection and result in locally heavier rainfall over these mostly
urban areas. Meanwhile over the Gold Coast, a local minimum of
rainfall may develop, but the heavy rain there the past couple days
as well as some chance of shower and thunderstorm activity may
cause widely scattered localized flooding. No changes were made to
the ERO risk areas.

Wegman


Day 3
Valid 12Z Wed Oct 09 2024 - 12Z Thu Oct 10 2024

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR CENTRAL AND
NORTH FLORIDA AS WELL AS FAR SOUTHEASTERN GEORGIA...

The main circulation of Hurricane Milton will cross the Florida
Peninsula on Wednesday. There remains considerable uncertainty as
to where the center will make landfall, which will of course play a
huge role as to where the heaviest rainfall amounts will be. See
the NHC forecast for the latest track. The storm is expected to be
undergoing increasing shear, beginning extratropical transition,
growing in size, and ingesting dry air. Thus, there is decent
agreement that at landfall, the storm will be weakening. This
should help to reduce the rainfall south of the circulation center
as dry air ingestion associated with extratropical transition
should quickly erode the rain-producing storms southwest of the
center. Very dry air behind a southward moving front will greatly
cut into rainfall amounts on the northern fringe of the
circulation. Thus, expect there to be a tight gradient of rainfall
both on the south and north sides of the circulation, but for
different reasons. The ERO risk areas have been expanded in both
directions due to track and storm size uncertainties, especially
towards the north, with the Moderate Risk expanded into far
southeastern Georgia, and the surrounding Slight and Marginal
expanded into the Low Country of coastal southern South Carolina.
This may be optimistic, but these expansions were made primarily
due to uncertainties, and will likely be refined in the coming
days.

For the moment, there are several reasons a High Risk was not
considered in no particular order: 1) The storm will be weakening
prior to landfall which may temper rainfall amounts a little bit,
2) Milton's small size should reduce the areal coverage of the
heaviest rain, 3) The primary rain footprint of Milton over north
Florida will largely miss where the hardest hit areas of the PRE in
south Florida are. Of course there is some overlap, but not nearly
as much as with Helene, 4) The core of the heaviest rain at the
moment is expected to track from north of Tampa northeast through
around Jacksonville. This area has been relatively dry in recent
days compared to areas further south, 5) Milton will be moving
quickly and accelerating. This will reduce the time the heaviest
rain has along and north of the track to result in widespread and
numerous flash floods, 6) The inclusion of CAMs and higher
certainty with the track may help to narrow down where a potential
High Risk may be needed with future forecasts. For now with Day 3
being outside the CAMs time range, the large Moderate will
suffice.

Wegman
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FOUS30 KWBC 030828
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
428 AM EDT Thu Oct 3 2024

Day 1
Valid 12Z Thu Oct 03 2024 - 12Z Fri Oct 04 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

The latest guidance continues to have heavier QPF over the
Southeast Louisiana Parishes with areal averages of 2 to 3 inches
for areas along and south of I-10 from near New Orleans through
Biloxi towards Mobile, with some of the CAMs as much as 3 to 5
inches near the coastline. Spread persists in the placement of the
local maxima with the highest potential likely over either St.
Bernard or Plaquemines Parishes, both areas that are very difficult
to flood due to the swampy land structures and sandier soils that
limit flash flood potential.

Campbell


Day 2
Valid 12Z Fri Oct 04 2024 - 12Z Sat Oct 05 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

During this period there will be broad cyclonic over the Western
Gulf along with deep tropical air that advects into the flow. This
will result in convection that breaks out across the Gulf and
creeps inland into South Texas. A majority of the guidance
maintainsthe highest QPF offshore however there could be 0.75 to
1.5 inches that occurs in South Texas that should provide
beneficial moisture to the area rather than pose as an threat for
local flooding concerns.

Campbell


Day 3
Valid 12Z Sat Oct 05 2024 - 12Z Sun Oct 06 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Campbell

d
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FOUS30 KWBC 040733
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
333 AM EDT Fri Oct 4 2024

Day 1
Valid 12Z Fri Oct 04 2024 - 12Z Sat Oct 05 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Wegman


Day 2
Valid 12Z Sat Oct 05 2024 - 12Z Sun Oct 06 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Wegman


Day 3
Valid 12Z Sun Oct 06 2024 - 12Z Mon Oct 07 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR SOUTHWEST
FLORIDA AND THE LOWER KEYS...

A tropical wave or weak and slow-moving disturbance over the Gulf
will drift east into the Florida Peninsula Sunday. Multiple inches
of rain are expected through the day from Tampa south into the
Keys. The heaviest rain is expected Sunday afternoon and evening,
where added instability from diurnal heating will locally increase
rainfall rates. The slow-moving nature of any storms will be the
greatest contributor to flash flooding. FFGs have recovered since
Helene last week, so despite the forecast of 2-4 inches of rain
broadly over the Florida Gulf coast, only isolated flash flooding
is expected at this point.

Wegman
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FOUS30 KWBC 050745
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
345 AM EDT Sat Oct 5 2024

Day 1
Valid 12Z Sat Oct 05 2024 - 12Z Sun Oct 06 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR COASTAL DEEP
SOUTH TEXAS...

...Deep South Texas...

Easterly flow to the north of a developing but weak low over the
western Gulf that is the focus for widely scattered thunderstorm
activity over the Gulf is forcing storms to move inland from the
Gulf over Padre and South Padre Islands this morning. A cold front
will push south across Deep South Texas today, which will push the
tropical moisture south into Mexico, so the threat for flash
flooding is confined to the immediate coast down to Brownsville for
the day today. The flood threat should abate by tonight.

...South Florida...

The urban corridor of southeast Florida, including Miami may see
occasional heavy rain from westward-moving thunderstorms this
afternoon and evening. The storms should continue moving and weaken
as they move inland, so the threat while non-zero, should remain
under Marginal Risk levels. Better agreement in the CAMs may
necessitate a Marginal Risk issuance for this area with the midday
update.

Wegman


Day 2
Valid 12Z Sun Oct 06 2024 - 12Z Mon Oct 07 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR MUCH OF THE
SOUTHERN FLORIDA PENINSULA...

A trough developing ahead of a slowly developing tropical low over
the Gulf will form over the southern Florida Peninsula on Sunday.
The air mass the trough will be developing in will be incredibly moisture-rich...with PWATs anywhere from 2.2 to 2.6 inches. This
will be close to the climatological maximum for this time of
year...between the 95th and 99th percentile and more than 3 sigma
above normal. The predominant mid-level wind flow will switch from northeasterly to southwesterly during the period, resulting in
chaotic storm motions. The heaviest rainfall totals will be along
both coasts, from Tampa south through Cape Coral on the Gulf Coast
as well as from the Treasure Coast south through Miami on the
Atlantic side. This bimodal distribution of QPF suggests
organization will be somewhat lacking, depending more on mesoscale
phenomena such as sea breezes or differential heating between the
urban areas and their surroundings.

This will likely be the first day of several where heavy rain will
be common and widespread across the Florida Peninsula. In the
increasingly likely event a tropical cyclone eventually develops in
the Gulf and moves towards the Florida Peninsula mid to late week,
this will be the first day of the predecessor rain event, or PRE.

Given high FFGs areally and this being the first day of the PRE, a
Marginal Risk was left intact for this area, but further increases
in forecast rainfall may require a Slight Risk for some of the
urban areas with future updates.

Wegman


Day 3
Valid 12Z Mon Oct 07 2024 - 12Z Tue Oct 08 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
FLORIDA PENINSULA...

Conditions across the Florida Peninsula will continue to
deteriorate on Monday. The PRE is expected to continue to
intensify, making for a second full day of periodic heavy rainfall
across the Peninsula. Both overall rainfall amounts and coverage
north up the Peninsula will increase on Monday as compared with
Sunday. All but the fastest guidance suggest that should a tropical
cyclone form over the Gulf, it will remain well west of the Florida
Peninsula through Monday night. This means the PRE will remain in
full force across the Peninsula. Once again, there will be a
bimodal distribution of the precipitation...but much more
pronounced. The focus will remain along both coasts, albeit heavier
and spread north. Given the expected heavy rainfall from Day
2/Sunday, by Monday most soils should be at or near saturation.
This means most of the day's rains will convert to runoff in most
areas.

With heavier rainfall expected in the urban areas along both
coasts, a Slight Risk upgrade was introduced with this update, in
coordination with MFL/Miami, FL; TBW/Tampa, FL; and MLB/Melbourne,
FL forecast offices. With better definition as to how and where any
tropical cyclone may develop over the Gulf, this will improve the
forecast for the PRE on Monday. This will apply both to where the
heaviest rain may occur as well as how heavy the amounts will be.
Further, with the hindsight of where Sunday's rainfall will occur,
it's possible additional upgrades may be needed with future
forecasts...though a preponderance of the guidance suggests any
direct effects of a potential tropical cyclone will hold until
after this period. Depending on how the heaviest rain areas align
on Monday with Sunday, some areas may be approaching 2 day totals
of 10 inches of rain by Tuesday morning. These amounts of rain in
any urban areas could approach Moderate Risk level impacts.

Wegman
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FOUS30 KWBC 220834
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
434 AM EDT Sun Sep 22 2024

Day 1
Valid 12Z Sun Sep 22 2024 - 12Z Mon Sep 23 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE MID MISSISSIPPI VALLEY TO THE SOUTHERN HIGH PLAINS...

The focus for areas of heavy rainfall will continue to be within a
plume of deeper moisture ahead of a large-scale upper trough making
its way out over the plains towards the Mid-Mississippi Valley. The
airmass already in place had precipitable water values generally
at or above 1,75 inches...from the western portion of Texas
northeastward to where it encounters a cold front moving in from
the northern United States. Latest model runs still support two
areas of more concentrated rainfall warranting a Slight Risk area--
namely over western Texas and from southern Missouri into southern
Illinois. The southern area should be more driven by diurnal
instability strong enough to support spotty 2 or 3 inch rainfall
amounts and rainfall rates topping an inch per hour. The area
farther east will have the added advantage of a surface front to
help focus moisture convergence but the upper support is not
expected to be as strong as it was on Saturday. For that
reason...confidence in occurrence is somewhat diminished. Made a
small southward adjustment to the Slight Risk area based on latest
guidance and a trimmed a bit of the northern periphery of the
Marginal given the placement of the cold front.

Bann


Day 2
Valid 12Z Mon Sep 23 2024 - 12Z Tue Sep 24 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE MID MISSISSIPPI VALLEY...

Surface low pressure begins to develop on Monday as shortwave
energy moving through the southern stream trough...leading to
renewed showers and thunderstorms in the Mid-Mississippi Valley
early in the day that shifts into the Ohio Valley by late Monday
night/early Tuesday morning. The best overlap of ingredients and
forcing looks appears to be from the afternoon into the early
evening across portions of southeast Missouri into parts of
southern Illinois. After that...low level flow should take on an
increasing component parallel to the front. Between the weakening
magnitude of moisture flux convergence at the front and the loss of
daytime heating/destabilization...rainfall rates should be waning.
There are a few ensemble members which generate over an inch of
rain over the Ohio Valley as upper flow backs in response to energy
in the northern stream...but the expectation is that the flash
flooding risk is minimal with those rainfall rates and dry
antecedent conditions.

Bann


Day 3
Valid 12Z Tue Sep 24 2024 - 12Z Wed Sep 25 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE Eastern OHIO VALLEY AND ACROSS CENTRAL OF WESTERN TEXAS...

Ohio Valley...
As energy in the southern stream interacts with digging energy in
the northern stream late on Day2...the flow begins to back and
become diffluent leading to increasing coverage of rainfall by the
time Day 3 begins. The flow should continue to become increasingly
diffluent aloft with precipitable water values now about 1.75
inches in place. Spaghetti plots of QPF from the ensembles show
minimal support for amounts greater than 2 inches...and most of
that support is from just a few GEFS members. With antecedent
conditions being so dry...it is presumed that only isolated
instances will occur that run off problems occur.

Texas
Light southeasterly on-shore flow across far southern Texas will
start to draw moisture northward again on Tuesday afternoon. As it
does so..a weakening cold front will help provide some focus for
showers and a few thunderstorms in central or western Texas. The
NAM and ECMWF were the only two operational runs from the 22/00Z
model suite to generate 2+ inch amounts of QPF while the GFS had
support from the GEFS favoring a weaker/drier solution. Given the uncertainty...opted to maintain a Marginal risk for this cycle.

Bann
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FOUS30 KWBC 230815
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
415 AM EDT Mon Sep 23 2024

Day 1
Valid 12Z Mon Sep 23 2024 - 12Z Tue Sep 24 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE MID-MISSISSIPPI VALLEY EASTWARD TO THE SOUTHERN APPALACHIANS...

Precipitation over the southern Plains will continue to spread
north ahead of a positively-tilted upper shortwave trough drifting
east through the central Plains. Deepening moisture (PWs ~1.75-2
inches) supported by southwesterly inflow, and large-scale ascent
generated by the upper shortwave, are expected to produce a broad
area of precipitation spreading northeast early in the period from
the Ozarks through the lower Missouri and mid Mississippi valleys.
There is the potential for a stripe of locally heavy amounts, with
the 00Z HREF showing high neighborhood probabilities for
accumulations of 3 inches or more from central Missouri eastward
through the St. Louis metro. However, limited instability should
help to keep rainfall rates in check through the morning hours. A
better chance for heavy rainfall rates may develop later in the day
as trailing energy and daytime heating contribute to storms
redeveloping near the Ozarks and tracking northeast through the mid
Mississippi Valley and into the lower Ohio Valley later this
afternoon into the evening.

Moisture spreading further east is expected to fuel showers and
storms developing later today across the central and southern
Appalachians. Some of the hi-res guidance continue to show some
potential for isolated heavy amounts across the region, with the
greatest threat centered over western North Carolina, where the
HREF is showing high neighborhood probabilities for accumulations
of 2 inches or more.

Pereira


Day 2
Valid 12Z Tue Sep 24 2024 - 12Z Wed Sep 25 2024

..THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE OHIO VALLEY AND THE CENTRAL TO SOUTHERN APPALACHIANS...

The shortwave trough moving across the mid Mississippi Valley on
Day 1 will begin to interact with a northern stream trough
amplifying over the northern Plains early in the period. Models
show the upper pattern quickly amplifying over the Mississippi
Valley on Tuesday. At the surface, low pressure is expected to
track northeast from the mid Mississippi Valley to the Great Lakes,
with a trailing cold front extending back through the Ohio Valley.
An axis of deeper moisture (PWs ~1.50-1.75 inches) coinciding with
deep southeasterly flow ahead of the upper trough will fuel
showers and storms along the low track and ahead of the trailing
cold front. Models do not present a signal for widespread heavy
amounts but show the potential for locally heavy amounts,
including for portions of the central to southern Appalachians,
where relative soil moisture is slightly higher and flash flood
guidance values lower.

Pereira


Day 3
Valid 12Z Wed Sep 25 2024 - 12Z Thu Sep 26 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE SOUTHEAST, TENNESSEE VALLEY, AND THE SOUTHERN APPALACHIANS...

Although disagreements on the track continue, the consensus of the
models show a powerful tropical cyclone tracking north through the
eastern Gulf of Mexico during this period. Apart from the faster
Canadian solutions, which bring heavy amounts into the Florida
Panhandle, most of the deterministic models and their ensemble
means show moderate to heavy rains brushing the coast, but the
heaviest amounts remaining out over the open waters through 12Z
Thu. Therefore, just a Marginal was maintained from South Florida
and the Keys northward along the Florida Gulf Coast through the
Panhandle. However, should more guidance begin to trend toward a
faster solution, future upgrades may be necessary.

Despite their disagreements with the cyclone track, the models are
presenting a growing signal for heavy amounts developing well to
the north. The cold front pushing east into the Ohio, Tennessee,
and lower Mississippi Valley prior to the period is forecast to
slow across the region, providing a focus for moisture ushered in
by strong southeasterly to easterly flow ahead of the system. With
some longitudinal disagreement, the GFS and ECMWF show PWs
increasing to 1.75-2 inches along an axis of strong low level
convergence extending north from the northern Gulf Coast into the
Tennessee Valley. Meanwhile, an upper low that will begin to
develop over the mid Mississippi Valley on Wednesday is expected to
drop south, enhancing lift across the region. While there is some
west-east disagreement on its placement, most of the 00Z
deterministic runs showed a stripe of 2-4 inch accumulations
extending northeastward from northern Alabama into the southern
Appalachians.

Pereira
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FOUS30 KWBC 240826
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
426 AM EDT Tue Sep 24 2024

Day 1
Valid 12Z Tue Sep 24 2024 - 12Z Wed Sep 25 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE OHIO/Tennessee VALLEYS AND ADJACENT PORTIONS OF THE MID-ATLANTIC ...

One area of showers and thunderstorms that produced spotty moderate
to heavy rainfall overnight along a quasi-stationary front
overnight should be weakening as it reaches portions of the Mid-
Atlantic region by morning. However...shortwave energy in the
northern stream will be developing a closed low that deepens with
time as it tracks from the Upper Midwest into the Mid-Mississippi
Valley later tonight. This backs the flow aloft and supports some
convection with locally heavy rainfall rates in a diffluent flow
regime over the eastern Ohio Valley as well as thunderstorms ahead
of the low track and ahead of a trailing cold front. Model guidance
continues to show the potential for locally heavy amounts while not
presenting a signal for widespread heavy rainfall
totals...including portions of the central and southern
Appalachians where relative soil moisture is slightly higher and
where flash flood guidance was lower.

Bann


Day 2
Valid 12Z Wed Sep 25 2024 - 12Z Thu Sep 26 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE SOUTHEAST UNITED STATES AND EASTERN TENNESSEE VALLEY...

Only minor adjustments were needed to the previously issued Slight
risk area from portions of Alabama and Georgia into southeast
Tennessee...while a targeted Slight Risk area was introduced along
the coastline of the Florida panhandle. It appears that a
predecessor rainfall event will take shape somewhere in the
Southeast US as moisture streams northward from the Gulf of Mexico
ahead of Potential Tropical Cyclone Nine and interacts with a cold
front dropping southward from the Tennessee Valley. There is still
some disagreement among the various models with respect to where
the axis may set up but the area covered by the Slight risk has the
best overlap of different solutions so only minor adjustments were
needed to what is effectively a high-end Slight Risk area. Along
the coast...model QPF has increased along portions of the Florida
coastline to the point where a Slight seems warranted.

Bann


Day 3
Valid 12Z Thu Sep 26 2024 - 12Z Fri Sep 27 2024

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE SOUTHEAST UNITED STATES AT POTENTIAL TROPICAL CYCLONE NINE
MOVES INLAND...

There should be an increasing threat of widespread and potentially
significant rainfall as Potential Tropical Cyclone Nine approaches
the coast and eventually makes landfall sometime around 27/00Z
based on the latest guidance from the National Hurricane Center.
Moderate to heavy rainfall may develop across portions of Florida
panhandle into the Southeast US well before PTC Nine make landfall
as strong transport of Gulf moisture interacts with deepening mid-
and upper-layer closed low over the central/southern Mississippi
Valley. Primary changes were to extend the Moderate risk area
northward along the NHC path of PTC Nine where the guidance had
shown an increase in rainfall amounts...with the Moderate risk now
into the southern Appalachians where terrain effects look to result
in locally enhanced rainfall amounts.

With an unusually deep low best seen in the mid- and upper-levels
located to the west...at least some of the moisture being drawn
inland by Nine will begin to get drawn westward over portions of
the Tennessee Valley and into the Mississippi Valley. As a
result...part of the Slight risk area from the Southeast US gets
pulled westward into the Tennessee Valley around the mid- and
upper-level low. Given the model spread and the poor run to run consistency...refrained from taking the Slight risk area too far
westward at this point.

Bann
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FOUS30 KWBC 241659
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1259 PM EDT Tue Sep 24 2024

Day 1
Valid 16Z Tue Sep 24 2024 - 12Z Wed Sep 25 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE VIRGINIA/NORTH CAROLINA PIEDMONT NEAR THE STATE LINE...

...16Z Update...

...VA/NC border...

In coordination with RNK/Blacksburg, VA; RAH/Raleigh, NC; and
AKQ/Wakefield, VA forecast offices, a Slight Risk area was
introduced with this update along the VA/NC border in the Piedmont
area. Tonight, much of the guidance, including the 12Z HRRR, HREF,
and both ARWs are suggesting an area of training convection will
develop. The heavy rain will be forced by a stationary surface
trough over the area combined with a local maximum of atmospheric
moisture with PWATs over 1.75 inches. A strong and deep upper level
trough over the Mississippi Valley will greatly increase the upper
level divergence to its east. This too will greatly add lifting
support to the storms as they form with the convective maximum
after sunset this evening. HREF probabilities are up to 30% of
exceeding FFGs in the western part of the Slight risk area, as well
as over 80% of exceeding 3 inches of rain in the neighborhood
probabilities and almost 50% of exceeding 5 inches through
tonight.

The factors working against heavy rain and flash flooding are some
antecedent dry conditions, with at least average soil moisture
across this area, and marginal instability generally around 500 to
1,000 J/kg. The instability will limit to some extent the
widespread coverage of the heavy rain, but the excellent forcing
may be able to make up for that. Portions of the Slight Risk area
saw heavy rainfall last week, which at least has kept those area
from having totally dry soils...but average soil moisture can
sometimes work against flash flooding as some clays can be
hydrophobic when they're really dry, resulting in extra runoff.
Such is not expected to be the case here.

...Midwest...

Elsewhere across the Upper Ohio and Tennessee Valleys expect
continued off and on showers and storms, but general struggles with organization. Very dry soils north of the Ohio River should also
generally limit the flooding threat...whereas along the west facing
slopes of the Appalachians, localized upslope may enhance it a bit.
Regardless any flash flooding in these areas should be confined to
urban and flood-prone locations.

Wegman

...Previous Discussion...

One area of showers and thunderstorms that produced spotty moderate
to heavy rainfall overnight along a quasi-stationary front
overnight should be weakening as it reaches portions of the Mid-
Atlantic region by morning. However...shortwave energy in the
northern stream will be developing a closed low that deepens with
time as it tracks from the Upper Midwest into the Mid-Mississippi
Valley later tonight. This backs the flow aloft and supports some
convection with locally heavy rainfall rates in a diffluent flow
regime over the eastern Ohio Valley as well as thunderstorms ahead
of the low track and ahead of a trailing cold front. Model guidance
continues to show the potential for locally heavy amounts while not
presenting a signal for widespread heavy rainfall
totals...including portions of the central and southern
Appalachians where relative soil moisture is slightly higher and
where flash flood guidance was lower.

Bann


Day 2
Valid 12Z Wed Sep 25 2024 - 12Z Thu Sep 26 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE SOUTHEAST UNITED STATES AND EASTERN TENNESSEE VALLEY...

Only minor adjustments were needed to the previously issued Slight
risk area from portions of Alabama and Georgia into southeast
Tennessee...while a targeted Slight Risk area was introduced along
the coastline of the Florida panhandle. It appears that a
predecessor rainfall event will take shape somewhere in the
Southeast US as moisture streams northward from the Gulf of Mexico
ahead of Potential Tropical Cyclone Nine and interacts with a cold
front dropping southward from the Tennessee Valley. There is still
some disagreement among the various models with respect to where
the axis may set up but the area covered by the Slight risk has the
best overlap of different solutions so only minor adjustments were
needed to what is effectively a high-end Slight Risk area. Along
the coast...model QPF has increased along portions of the Florida
coastline to the point where a Slight seems warranted.

Bann

Day 3
Valid 12Z Thu Sep 26 2024 - 12Z Fri Sep 27 2024

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE SOUTHEAST UNITED STATES AT POTENTIAL TROPICAL CYCLONE NINE
MOVES INLAND...

There should be an increasing threat of widespread and potentially
significant rainfall as Potential Tropical Cyclone Nine approaches
the coast and eventually makes landfall sometime around 27/00Z
based on the latest guidance from the National Hurricane Center.
Moderate to heavy rainfall may develop across portions of Florida
panhandle into the Southeast US well before PTC Nine make landfall
as strong transport of Gulf moisture interacts with deepening mid-
and upper-layer closed low over the central/southern Mississippi
Valley. Primary changes were to extend the Moderate risk area
northward along the NHC path of PTC Nine where the guidance had
shown an increase in rainfall amounts...with the Moderate risk now
into the southern Appalachians where terrain effects look to result
in locally enhanced rainfall amounts.

With an unusually deep low best seen in the mid- and upper-levels
located to the west...at least some of the moisture being drawn
inland by Nine will begin to get drawn westward over portions of
the Tennessee Valley and into the Mississippi Valley. As a
result...part of the Slight risk area from the Southeast US gets
pulled westward into the Tennessee Valley around the mid- and
upper-level low. Given the model spread and the poor run to run consistency...refrained from taking the Slight risk area too far
westward at this point.

Bann
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FOUS30 KWBC 250903
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
503 AM EDT Wed Sep 25 2024

Day 1
Valid 12Z Wed Sep 25 2024 - 12Z Thu Sep 26 2024

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE SOUTHEAST UNITED STATES...

Even though Helene should still be well off-shore during the
period...abundant moisture should be streaming northward ahead of
the storm. The models have been increasingly aggressive with
rainfall amounts coming off the Gulf into the Florida panhandle
with locally excessive amounts of rainfall along the coastline. Of
greater concern is the moisture that continues to stream northward
into portions of northern Georgia and upstate South Carolina where
a surface cold front acts to focus a predecessor rainfall event.
Some pieces of guidance...including the HAFS A and B parent grids
...drop 5 or 6 inches or rainfall within a broader area of 2 to 4
inches of rainfall. The overall agreement on placement of the axis
is really very good with only subtle east/west variations...which
necessitated an expansion of the moderate risk area and now
includes some of the complex terrain of the southern Appalachians.
Slight and Marginal risk areas surrounding covered the risk of
convection forming along broad synoptic scale flow getting drawn
into the environment ahead of Helene.

Bann


Day 2
Valid 12Z Thu Sep 26 2024 - 12Z Fri Sep 27 2024

...THERE IS A HIGH RISK OF EXCESSIVE RAINFALL IN PORTIONS OF THE
SOUTHERN APPALACHIANS...

Given the increasing confidence about the overlap of the axis of
a predecessor rainfall event on Day 1 period and the amount of
rainfall expected as the center of Helene approaches the southern
Appalachians during the latter part of the Day 2 period...there has
been a growing number of models generating close to 10 or 11
inches of rainfall for the 2-days combined in the complex terrain.
That raises concerns about impactful flooding becoming widespread
with considerable and potentially life-threatening flash and urban
flooding as well as areas of significant river flooding over
portions of Florida, the Southeast U.S. and the southern
Appalachians. Widespread minor to moderate river flooding is likely
and major river flooding is possible. Landslides are possible in
areas of steep terrain in the southern Appalachians given these
rainfall amounts. This prompted the upgrade to a high risk over
portions of northwestern Georgia into far western South Carolina
that was mainly confined to the terrain. What effectively amounts
to a high-end moderate risk surrounds the high that extends along
much of the track as Helene makes landfall along the Florida
panhandle coastline around 27/00Z (give or take a couple of hours)
based on the latest NHC guidance. In terms of model guidance...the
tracks tended to be clustered well resulting in NHC guidance being
close to most model runs. For the Day 2 period...that resulted in
the highest rainfall totals being close to each other where the
orographic forcing was consistent. A second axis of excessive
rainfall branched off to the northwest from Helene's track towards
a deep-layered low developing over the southern portion of the
Mississippi Valley as moisture gets entrained into that system
leading to scattered convection that could produce locally heavy
amounts. Mainly confined the Slight risk to the Tennessee Valley
and only a Marginal risk extending back towards the core of the
upper system.

Bann


Day 3
Valid 12Z Fri Sep 27 2024 - 12Z Sat Sep 28 2024

...INTRODUCED A MODERATE RISK OF EXCESSIVE RAINFALL OVER A PORTION
OF THE UPSLOPE REGION INTO THE SOUTHERN APPALACHIANS...

Based on latest NHC track guidance...Helene should be in northern
Georgia and tracking on a more northwestward course during the day.
This suggests the flow of deep moisture should be on-going to the
terrain of western Carolinas into southwest Virginia. Latest model
guidance shows several inches of rainfall in addition to what falls
in the predecessor 48 hours...felt a focused Moderate risk placed
where there was best model consensus was warranted. It was also a
multi-day rainfall total farther south along the NHC track in the
eastern Tennessee Valley that was the main reason to keep a Slight
Risk where model QPF be a little too light to support one. That
portion of the Slight Risk area extends westward to the deep-
layered low where steepening low level lapse rate and the
additional moisture streaming off of Helene could lead to some
showers and thunderstorms capable of producing locally heavy
downpours.


Bann
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FOUS30 KWBC 280758
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
358 AM EDT Sat Sep 28 2024

Day 1
Valid 12Z Sat Sep 28 2024 - 12Z Sun Sep 29 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR MUCH OF THE
OHIO AND TENNESSEE VALLEYS AS WELL AS FOR CENTRAL FLORIDA...

...Ohio/Tennessee Valleys...

The combined upper low and remnant circulation of what is left of
Helene is expected to slow/stall over the Ohio and Tennessee
Valleys. With very little if any instability to work with the bulk
of rain today will likely be stratiform with hourly rates around
0.5 inch/hour or lower. At best there may be some isolated flash
flooding, therefore maintained the broad Marginal Risk that is in
place over the region.

...Florida...

A trailing cold front across the Florida peninsula will be present
during this period along with abundant instability and moisture
within proximity to this feature. The development of strong
thunderstorms can be expected, especially on the western side of
the peninsula. Recent heavy rain has increased soil sensitivity for
much of the area therefore maintained a Marginal Risk for excessive
rainfall for the western and central peninsula.

Campbell


Day 2 Valid 12Z Sun Sep 29 2024 - 12Z Mon Sep 30 2024

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF
THE MID-ATLANTIC/APPALACHIANS AS WELL AS THE NORTHERN FLORIDA
PENINSULA...

...Mid-Atlantic/Central Appalachians...

During this period the remnant low of Helene will get picked up by
the upper level jet and track eastward into the Mid-Atlantic and Central/Northern Appalachians. There will be an increase in
available instability which may lead to localized enhanced rainfall
rates for portions of the Shenandoah Valley and west to the
Allegheny Front in Maryland, West Virginia, and Virginia; which may
result in isolated to widely scattered instances of flash
flooding. The level of threat continues to be handled well with the
Marginal Risk that is currently in effect. There may be a need for
a Slight Risk with future updates depending on model trends and
observations.

...Florida...

Convection will continue to fire up in proximity to a stalled
frontal boundary draped across northern/central Florida. Storm
motion may be fast-moving with some tracking over areas hard-hit
by Helene, but because progressive nature of the convection a
Marginal Risk remains appropriate for this period.

Campbell


Day 3
Valid 12Z Mon Sep 30 2024 - 12Z Tue Oct 01 2024

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF
THE MID-ATLANTIC/CENTRAL APPALACHIANS...

The lingering upper low over the East and accompanying moisture
from Helene will continue to produce some showers and thunderstorms
over portions of the Appalachians and Mid-Atlantic into Monday.
Heavy intensity and accumulations are not expected to be widespread
or heavy, however the recent wet period keeps an elevated threat
for excessive rainfall and isolated flooding concerns. A Marginal
remains in effect from south-central Virginia to central
Pennsylvania.

Campbell
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FOUS30 KWBC 290815
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
415 AM EDT Sun Sep 29 2024

Day 1
Valid 12Z Sun Sep 29 2024 - 12Z Mon Sep 30 2024

...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF
THE INTERIOR MID-ATLANTIC...

...Mid-Atlantic/Central Appalachians...

Remnant moisture from Helene will remain caught up in the upper
trough pattern across the Ohio Valley while the mean trough begins
to slowly advance eastward through the period. During this period
precipitable water anomalies will be on the order of 1 to 2
standard deviations above normal and will encounter increased
forcing from the upper jet and modest lift through the column over
much of the Mid-Atlantic. This setup will support the development
of scattered to numerous thunderstorms that will likely have slower
storm motions. Recent rains have lowered local FFGs and increased
sensitivity across the region. Areal average QPF for the region
will be in the 1 to 3 inch range with isolated maximums in excess
of 3 inches will be possible. A Slight Risk for excessive rainfall
is in effect for extreme western Maryland, eastern West Virginia, northern/central/south-central Virginia and north-central North
Carolina. A Marginal Risk area spans from northeast
Georgia/northwest South Carolina to southern Pennsylvania and
southeast Ohio.

...Florida...

An unstable airmass coupled with lingering deep layer moisture
will promote isolated to widely scattered thunderstorm activity
capable of localized flooding, especially within urbanized zones.
Any of these storms will have the capability to produce 2 to 4
inches, especially along the coastline. A Marginal Risk for
excessive rainfall is in effect for central portions of the
peninsula.

Campbell


Day 2
Valid 12Z Mon Sep 30 2024 - 12Z Tue Oct 01 2024

...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF
THE INTERIOR MID-ATLANTIC...

High pressure to the north, and a developing surface reflection
off the Mid-Atlantic coast thanks to the upstream trough will
create a persistent northeasterly flow setup with greater upslope
emphasis within the terrain across Western Virginia into the
far eastern West Virginia. There will be an enhancement of forcing
through the column of atmosphere near the Appalachian/Blue Ridge
spine that may result in hourly rainfall rates of 1 to 1.5
inches/hour during this period. Soils near saturation from recent
rains will keep the threat for flash flooding elevated for much of
this region thus maintained a Slight Risk for excessive rainfall
for extreme south-central Pennsylvania, western Maryland, eastern
West Virginia and northern/central Virginia. A Marginal Risk area
spans from northeast Tennessee/northwest North Carolina to southern Pennsylvania.

Campbell


Day 3
Valid 12Z Tue Oct 01 2024 - 12Z Wed Oct 02 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.


Campbell
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FOUS30 KWBC 300809
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
409 AM EDT Mon Sep 30 2024

Day 1
Valid 12Z Mon Sep 30 2024 - 12Z Tue Oct 01 2024

...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF
EASTERN WEST VIRGINIA, VIRGINIA AND NORTHERN NORTH CAROLINA...

The latest guidance continues to show the south/southeast trend of
where the heaviest rain is expected to occur Monday across the
Virginias. During this time the slow moving upper low will be transferring
its energy to a coastal low feature located offshore Virginia and
North Carolina. This will likely lead to a prolonged local
enhancement in hourly rainfall rates near the Blue Ridge of 1 to
1.5 inches/hour during this period. Soils near saturation from
recent rains will keep the threat for flash flooding elevated for
much of this region. A Slight Risk for excessive rainfall remains
in effect for extreme eastern West Virginia, northern/central
Virginia, and north-central North Carolina. The Marginal Risk was
extended to cover much of coastal North Carolina in association
with the developing coastal low potentially locally increasing
rainfall totals due to slow- moving convection especially on the
western side of Pamlico Sound.

Campbell


Day 2
Valid 12Z Tue Oct 01 2024 - 12Z Wed Oct 02 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Campbell


Day 3
Valid 12Z Wed Oct 02 2024 - 12Z Thu Oct 03 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Campbell
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FOUS30 KWBC 011241
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
841 AM EDT Tue Oct 1 2024

Day 1
Valid 12Z Tue Oct 01 2024 - 12Z Wed Oct 02 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR SOUTHEAST
Virginia INTO NORTHEAST NORTH CAROLINA AS WELL AS FOR CENTRAL FLORIDA...

...Virginia/North Carolina...

During this period an area of low pressure will slide off the
Virginia and North Carolina coast while periods of heavy rainfall
persists from Richmond south and east through Hampton Roads and
portions of far northeastern North Carolina and the northern Outer
Banks. A majority of the rain is expected through about mid-
afternoon. Rain amounts and coverage with decrease as the low moves
further offshore. The inherited Marginal Risk was maintained albeit
with minor adjustments to reflect the latest model guidance and
WPC forecast.

...Central Florida...

A disturbance moving along the stationary front over central
Florida may support more widespread shower and thunderstorm
activity from Tampa through Orlando to the Space Coast Tuesday
afternoon. Training of the convection and impacts with the urban
centers may result in isolated flash flooding. The inherited Marginal
Risk was maintained with a minor southward expansion.

Campbell/Wegman


Day 2
Valid 12Z Wed Oct 02 2024 - 12Z Thu Oct 03 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

There will be a lingering potential for convection near the
eastern coastline that could result in bursts of modest or very
local heavy rainfall intensities. The threat for excessive rainfall
and flooding concerns will remain below the 5 percent threshold for
this period.

Campbell


Day 3
Valid 12Z Thu Oct 03 2024 - 12Z Fri Oct 04 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

There is a non zero possibility for locally modest to heavy
rainfall to move northward from the Gulf of Mexico along the Gulf
Coast anywhere from the Mississippi River delta to west of the
Florida bend. There is a fair amount of model spread that further
serves to decrease confidence on where any of these storms may
occur. At this time a trends suggest that the bulk of the heaviest
rainfall will remain south of the coastline.

Campbell
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FOUS30 KWBC 020757
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
357 AM EDT Wed Oct 2 2024

Day 1
Valid 12Z Wed Oct 02 2024 - 12Z Thu Oct 03 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

There will be a lingering potential for convection near the
eastern coastline that could result in bursts of modest or very
local heavy rainfall intensities. The threat for excessive rainfall
and flooding concerns will remain below the 5 percent threshold for
this period.

Campbell/Hamrick


Day 2
Valid 12Z Thu Oct 03 2024 - 12Z Fri Oct 04 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

For a few days now there has been a signal for moderate to possibly locally heavy rainfall to move northward from the Gulf of Mexico into far
southeast portions of Louisiana and up near the Mississippi River
delta. This is associated with moisture convergence along a quasi-
stationary frontal boundary over the northern Gulf of Mexico. There
have been a fair amount of spread on where and how much will occur
and that has not resolved much for this round of guidance. In
general consensus keeps the highest QPF over the Gulf while a
couple of solutions suggest 2-3+ inches may reach the coastal water
and the wetlands. In coordination with the local forecast office
in New Orleans the forecast QPF will likely not lead to any impacts
of significance for the wetland areas of southeast Louisiana
especially given their recent drier stretch. The Marginal Risk area
was removed for this period.

Campbell


Day 3
Valid 12Z Fri Oct 04 2024 - 12Z Sat Oct 05 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

As mentioned during the Day 2 period there has been a multi-day
pattern where the convection is just offshore the Gulf Coast but
within the convection there could be a few inches of isolated heavy
rainfall. The spread for this period favors a placement more over
the Gulf than the Gulf Coastline. There is a non zero potential for
localized moderate, possibly heavy rainfall intensities however
nothing that is expected to become problematic at this time.

Campbell
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FOUS30 KWBC 150755
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
255 AM EST Fri Nov 15 2024

Day 1
Valid 12Z Fri Nov 15 2024 - 12Z Sat Nov 16 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Campbell


Day 2
Valid 12Z Sat Nov 16 2024 - 12Z Sun Nov 17 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Campbell


Day 3
Valid 12Z Sun Nov 17 2024 - 12Z Mon Nov 18 2024

...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF
THE SOUTHERN PLAINS...

An upper trough traversing through the West this weekend is
expected to split which will send energy in the Northern
Plains/Upper Midwest along with a strong southern stream cutoff low
into the Four Corner that will exit into the Central/Southern
Plains for the start of the week. A surface low pressure system
will forecast to spin up in the lee of the Rockies and deepen as it
tracks from the Plains through the Midwest. Scattered to widespread
moderate to heavy rainfall will be supported by this setup across
portions of the Southern Rockies and the adjacent Southern/Central
Plains.

Guidance is suggesting 1 to 2 inches of rain for central and
eastern portions of New Mexico, particularly over some of the same
areas that had several inches of snow last week. With rain on top
of snow expected some locations will have an increased risk for
flooding concerns. The Marginal Risk area that was already in
effect was expanded westward to now cover central and eastern
portions of New Mexico. The highest concentration of rainfall will
likely focus across parts of northern Texas/panhandle into western
Oklahoma. Consensus suggests areal average of 3 to 4.5 inches with
locally higher amounts possible. Therefore, a Slight Risk was
introduced with this issuance.

Campbell

$$
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FOUS30 KWBC 161558
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1058 AM EST Sat Nov 16 2024

Day 1
Valid 16Z Sat Nov 16 2024 - 12Z Sun Nov 17 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR THE COASTAL
RANGES OF THE PACIFIC NORTHWEST...

Conventional GOES satellite imagery along with ALPW data shows an
offshore atmospheric river beginning to gradually impinge on the
Pacific Northwest. An offshore warm front will gradually begin to
overspread the region by this evening which will coincide with
strong warm air advection and moisture transport. The latest 12Z
HREF guidance suggests a 40 to 50+ kt low-level jet arriving with
an orientation gradually becoming more orthognal to the coastal
terrain of western WA including the Olympic Peninsula and extending
southward down into northwest OR. A cold front will then begin to
approach and gradually cross western WA by 12Z/Sunday. This
atmospheric river event will be progressive, but there will be a
corridor of IVT values locally exceeding 500 kg/m/s tonight across
these coastal ranges based off the 06Z GFS which seems reasonable
considering the elevated CIRA-LVT parameters offshore. Some
rainfall rates associated with the combination of strong warm air
advection and orographic forcing should reach into the 0.25" to
0.50"/hour range between 00Z and 12Z, and this will help facilitate
some rainfall totals of 2 to 3 inches by 12Z for the windward
slopes of the coastal ranges. Given the expected rates and totals
by early Sunday morning, and thus earlier arrival of this event, a
Marginal Risk of excessive rainfall has introduced for this period.

Orrison


Day 2
Valid 12Z Sun Nov 17 2024 - 12Z Mon Nov 18 2024

...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF
THE SOUTHERN PLAINS...

A southern stream cutoff low is expected to eject into the Plains
and be accompanied with very impressive IVT, PWs and forcing as it
moves across Texas and Oklahoma by Sunday evening into the
overnight hours. This should be enough to overcome the limited
forecast instability and result in deep convection and heavy
rainfall rates across portions of the Southern Rockies and the
adjacent Southern/Central Plains. Guidance continues to suggest
2-4" of rain, but would expect isolated swaths as high as 4-6"
within this setup. The overall progressive nature of the system and
limited instability will cap the upper bound of rainfall
totals...but this system is dynamic enough with plentiful moisture
to suggest at least localized flash flooding is likely. A Marginal
Risk area remains in effect for central/eastern New Mexico,
northern Texas, most of Oklahoma and southern Kansas. The inherited
Slight Risk area saw a minor expansion to reflect the latest trends
and WPC QPF and spans from northern Texas/panhandle to western
Oklahoma.

...Coastal Oregon and northwest California...

A fairly progressive, weak/moderate atmospheric river will be
ongoing across the region. Total rain of 2-4" (through 12z Mon)
and hourly rainfall rates possibly approaching 0.5" within a narrow
southward shifting axis suggest that some minor flooding issues
could arise along coastal areas/mountains. A Marginal Risk area
remains in effect along the coastline.

Campbell


Day 3
Valid 12Z Mon Nov 18 2024 - 12Z Tue Nov 19 2024

...THERE ARE MARGINAL RISKS FOR EXCESSIVE RAINFALL FOR PORTIONS OF
THE GULF COAST AND THE PLAINS/UPPER MIDWEST...

...Central U.S. ...

The precipitation shield will shift eastward as the cold front
advances further into the Plains. Moderate to locally heavy
rainfall is expected from northern Texas to southern Minnesota with
areal average of 1 to 3 inches. The higher amounts will likely
concentrate over eastern Kansas, eastern Nebraska and western Iowa.
A Marginal Risk area was maintained with minor adjustments for this
issuance.

...Gulf Coast...

A plume of enhanced tropical moisture will likely advect northward
through the Gulf of Mexico well in advance of tropical cyclone
Sara; which will increase the potential for heavy rain and
localized flooding concerns along portions of the Gulf Coast. A
Marginal Risk area is in effect from southeast Texas to southern
Mississippi.

Campbell
$$
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FOUS30 KWBC 171556
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1056 AM EST Sun Nov 17 2024

Day 1
Valid 16Z Sun Nov 17 2024 - 12Z Mon Nov 18 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE SOUTHERN PLAINS...

1600Z Update...

The 12Z HREF guidance along with 06Z RRFS/REFS output continues to
support a locally heavy rainfall event across areas of the southern
Plains by this evening and extending into the overnight period. There
has been some shift farther west with some of the swaths of heavy
rainfall potential across west TX as some of the individual CAMs
are supporting the heavier rainfall/convection along the immediate
cold front and in close proximity to the deepening surface low
that will be evolving across the TX High Plains tonight. However, a complication to the rainfall forecast is the downstream evolution
of convection along the front ahead of the surface low involving
areas of northwest TX through southwest to central OK. This is
where strong moisture convergence and forcing may foster a threat
for some training areas of convection that become aligned in a
southwest to northeast fashion. Overall, still expecting some
swaths of 2 to 4 inch rainfall totals, with isolated potential for
heavier amounts and especially across northwest TX into southwest
OK where the better convective training threat will exist. Given
the latest CAM guidance, the Slight Risk area has been expanded
somewhat to account for the varying modes of convective evolution
that are expected this evening and overnight.

Elsewhere, no changes have been made to the previous D1 outlook
including the Marginal Risk area across western OR where there
continues to be some lingering, but modest atmospheric river
activity.

Orrison

Previous Discussion...

...Southern Plains...

A southern stream cutoff low is expected to eject into the Plains
today with very impressive IVT and accompanying anomalous PWs and
forcing as it moves across Texas and Oklahoma by this evening into
the overnight hours. This looks to be enough to overcome the
limited forecast instability and result in deep convection and
heavy rainfall rates across portions of the Southern Rockies and
the adjacent Southern/Central Plains. Guidance continues to suggest
2-4" of rain (per latest HREF and WPC QPF), but would expect
isolated swaths as high as 4-6" within this setup (indicated by
some of the heaviest CAMs). The overall progressive nature of the
system and limited instability will cap the upper bound of rainfall
totals, but this system is dynamic enough with plentiful moisture
to suggest at least localized flash flooding is likely. A Marginal
Risk area remains in effect for central/eastern New Mexico,
northern Texas, most of Oklahoma and southern Kansas. The inherited
Slight Risk area saw only minor adjustments to reflect the latest
trends and WPC QPF and spans from northern Texas/panhandle to
western Oklahoma.

...Coastal Oregon and northwest California...

A fairly progressive, weak/moderate atmospheric river will be
ongoing across the region. Total rain of 2-4" (through 12z Mon)
and hourly rainfall rates possibly approaching 0.5" within a narrow
southward shifting axis suggest that some minor flooding issues
could arise along coastal areas/mountains. A Marginal Risk area
remains in effect along the coastline.

Churchill/Campbell


Day 2
Valid 12Z Mon Nov 18 2024 - 12Z Tue Nov 19 2024

...THERE ARE MARGINAL RISKS OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE GULF COAST AND THE PLAINS/UPPER MIDWEST...

...Central U.S. ...

The precipitation shield will shift eastward as the cold front
advances further into the Plains. Moderate to locally heavy
rainfall is expected from northern Texas to southern Minnesota with
areal average of 1 to 3 inches. The higher amounts will likely
concentrate over eastern Kansas, eastern Nebraska and western Iowa.
A Marginal Risk area was maintained once again with only minor
adjustments for this issuance (not enough confidence for 2"+ totals
to introduce a Slight Risk).

...Gulf Coast...

A plume of enhanced tropical moisture will likely advect northward
through the Gulf of Mexico well in advance of tropical cyclone
Sara; which will increase the potential for heavy rain and
localized flooding concerns along portions of the Gulf Coast. A
Marginal Risk area is in effect from southeast Texas to southern
Mississippi (changed very little from inherited with 3" localized
totals possible).

Churchill/Campbell


Day 3
Valid 12Z Tue Nov 19 2024 - 12Z Wed Nov 20 2024

...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF
THE SOUTHEAST AND CENTRAL GULF COAST...

...Central Gulf Coast and Southeast...

By Tuesday significantly more tropical moisture will likely advect
northward through the Gulf of Mexico in association with the
remnants of Tropical Storm Sara; which will increase the potential
for heavy rain and localized flooding concerns along portions of
the Gulf Coast. An inherited Slight Risk area was maintained for
southern AL and surrounding portions of FL/GA/MS/LA, given the
potential for localized 3-5" totals (per ensemble guidance and WPC
QPF).

...Coastal Washington, Oregon, and northwest California...

Another weak/moderate atmospheric river is expected for region for
Day 3. Total rain of 2-4" (similar to Day 1) are expected with
hourly rainfall rates possibly approaching 0.5" once again suggest
that some minor flooding issues could arise along coastal
areas/mountains. An inherited Marginal Risk area remains in effect
along the coastline.

Churchill
$$
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FOUS30 KWBC 180756
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
256 AM EST Mon Nov 18 2024

Day 1
Valid 12Z Mon Nov 18 2024 - 12Z Tue Nov 19 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS SOUTHEAST
LOUISIANA INTO FAR SOUTHWEST MISSISSIPPI...


An axis of much above average tropical PW values expected to be
drawn rapidly northeastward from the remnants of Sara, across the
central Gulf of Mexico and into the Central Gulf coast ahead of
the negatively tilted closed low ejecting northeastward from the
Southern Plains into the Upper Mississippi Valley day 1. These
anomalous tropical PW values, 3 to 4+ standard deviations above the
mean will enhance convection along and ahead of the cold front
pushing eastward across the Gulf coast, primarily during the second
half of day 1 from southeast Louisiana into southern Mississippi.
A slight risk area was maintained where the latest HREF
neighborhood probabilities are highest for 2 and 3"+ amounts. The
simulated hi res radars are in good agreement in showing potential
for a period of training of cells in this anomalous PW axis in the
0000-1200 UTC Tuesday time period across the slight risk area of
southeast LA into southern MS. In areas of training, hourly
rainfall amounts of 1-2"+ possible, resulting in flash flooding,
especially in the urbanized areas of New Orleans.

Across the Southern to Central Plains toward the Upper MS Valley...there
is fairly good agreement on an axis of heavy rain from northern
OK, across much of KS, eastern NE, northwest MO, southeast SD, much
of IA, southern MN into southwest WI in a region of strong
isentropic lift ahead of the deepening surface low moving quickly
northeastward across these areas. While widespread heavy amounts
are likely, hourly rates will are mostly depicted as .25-50"+ in
the latest hi res guidance. This should keep the threat of any
runoff issues at marginal. The previous marginal risk area was
trimmed on the eastern end, taking out much of IA, MO and eastern
OK. The current marginal risk coincides well with the axis of the
highest HREF 2"+ day 1 probabilities.

Oravec

Day 2
Valid 12Z Tue Nov 19 2024 - 12Z Wed Nov 20 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM SOUTHEAST
LOUISIANA, ACROSS FAR SOUTHERN MISSISSIPPI, FAR SOUTHERN ALABAMA
INTO THE WESTERN FLORIDA PANHANDLE...

The convection that is expected to enhance along the Central Gulf
coast late day 1, will continue into day 2 as the surface front
continues to push east along the Gulf Coast. The tropical PW
values entrained ahead of this front day 1, will continue to push
across central to eastern Gulf coast day 2. Training of cells in a
southwest to northeasterly direction likely to continue Tuesday
morning from southeast LA into far southern MS, far southern AL and
the western FL Panhandle. There is some timing differences as to
whether heavy rains will continue in the vicinity of New Orleans
early Tuesday, or have pressed just to the east. The New Orleans
metro area was kept in the slight risk given potential for an
overlap of day 1 and day 2 heavy rain areas. The latest HREF 12
hour neighborhood probabilities ending 00Z Wed show the highest
probabilities for 2 and 3"+ amounts remaining across far southeast
LA, far southern MS, far southern AL and the western FL Panhandle.
This was the region depicted in a slight risk for day 2, with the
previous risk area trimmed on the northern end across south central
AL after collaboration with WFO MOB. The slight risk area
corresponds with the hi res consensus for the greatest hourly
totals of 1-2"+ in regions of training.

...Coastal Washington, Oregon and far northwest California...

Models are in good agreement with the rapid cyclogenesis event
across the northeast Pacific off the Pacific Northwest coast. The
low level southerly flow along and ahead of the associated cold
front will become very anomalous Tuesday night into early
Wednesday, with 850-700 mb moisture flux anomalies of 3-4 standard
deviations above the mean impacting the Pac NW/far northwest CA
coast. A well defined area of frontal precip likely to push inland
across coastal Pac NW/far northwest CA after 0000 UTC. Hourly
rainfall rates in the .25-50"+ range possible, especially across
southwest Oregon into far northwest CA where the strong southerly
low level flow will have a better upslope component. For areas of
northwest California into far southwest Oregon, this will be the
beginning of a multi day Atmospheric River event. No changes made
to the marginal risk area from the previous issuance.

Oravec


Day 3
Valid 12Z Wed Nov 20 2024 - 12Z Thu Nov 21 2024

...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL ACROSS FAR
Southwest OREGON INTO NORTHWEST CALIFORNIA...

The multi day atmospheric river event the began late day 2 for far
southwest Oregon into northwest California will continue day 3. The
rapidly deepening day 2 low over the northeast Pacific will anchor
a nearly stationary upper vortex off the Pac NW coast day 3. Strong
persistent deep layered west southwest flow on the south side of
this vortex will impact northwest California into far southwest
Oregon day 3. with IVT values of 500-800 km/m-1 s-2. and 850-700 mb
moisture flux anomalies of 2-4 standard deviations above the mean.
There is fairly good model agreement with heavy precip totals of
3-5" primarily over northwest California, with isolated totals of
6-8" possible. No significant changes made to the previous slight risk area.

Oravec

$$
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FOUS30 KWBC 190828
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
328 AM EST Tue Nov 19 2024

Day 1
Valid 12Z Tue Nov 19 2024 - 12Z Wed Nov 20 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE CENTRAL GULF COAST AND FOR PORTIONS OF NORTHWEST CALIFORNIA AND
SOUTHWEST OREGON...

...Central Gulf Coast...

Latest satellite imagery is showing enhancing convection to the
south of southeast LA associated with the anomalous tropical
moisture surge ahead of the cold front moving east across the
Central Gulf Coast. Trends in the latest hi res guidance suggest
this offshore enhancing convection will become the heaviest
frontal/pre-frontal rains as organized convection currently along
the front farther to the north begin to weaken after 1200 UTC. Hi
res guidance is in fairly good agreement that the heaviest rains
with the offshore enhancing convection will remain just to the
south of far southern MS, far southern AL and the western FL
Panhandle, but still affecting far southeast LA. HREF neighborhood probabilities show that the axis of the highest probabilities for 2
and 3"+ amounts will remain offshore with the northern edge of
these higher probabilities affecting areas from far southeast LA
and along the immediate far southern MS, far southern AL and
western FL Panhandle. Changes to the previous outlook were to trim
the northern extent of the slight risk area by approximately 20 nm
and to trim the western extent of the slight risk by
approximately 40nm to account for the hi res trends. At the
moment, the consensus on timing of convection supports removing the
New Orleans metro area from the slight risk, with the heaviest
rains likely to the east and southeast prior to 1200 UTC Tuesday.

...Coastal Washington, Oregon and far northwest California...

Latest models continue to be in good agreement on the rapid
cyclogenesis event across the northeast Pacific off the Pacific
Northwest coast, signaling the beginning of a multi day Atmospheric
River event for northwest CA into far southwest OR. Anomalous low
level southerly flow expected along and ahead of the associated
cold front Tuesday night into early Wednesday, with 850-700 mb
moisture flux anomalies of 3-4 standard deviations above the mean
impacting the coastal Pac NW, south into far northwest CA coast. A
well defined area of frontal precip likely to push inland across
coastal Pac NW/far northwest CA after 0000 UTC Wednesday. The
strong southerly low level flow will be mostly parallel to the
terrain along the Pac NW coast, limiting hourly rainfall rates to
.10-.25"+. Greater hourly rates likely across far southwest Oregon
into coastal NW CA where a more significant upslope component to
the low level flow is likely. Hi res guidance is fairly similar in
showing hourly rates of .25-.50"+ in the 0600 to 1200 UTC Wednesday
period across far southwest OR into far NW CA. HREF .50"/hr
probabilities subsequently are high across this area, with 1"/hr
probabilities much lower and primarily offshore. No changes made to
the previous slight risk area, which corresponds well to the above
mentioned axis of high .50"+/hr HREF neighborhood probabilities.

Oravec


Day 2
Valid 12Z Wed Nov 20 2024 - 12Z Thu Nov 21 2024

...THERE IS A MODERATE RISK FOR EXCESSIVE RAINFALL ACROSS PORTIONS
OF NORTHWEST CALIFORNIA...

The multi day atmospheric river event the began late day 1 for far
southwest Oregon into northwest California will continue day 2,
primarily across northwest California. The rapidly deepening low
over the northeast Pacific day 1 will anchor a nearly stationary
upper vortex off the Pac NW coast day 2. Strong persistent deep
layered west southwest flow on the south side of this vortex will
impact northwest California day 2, with IVT values of 500-800
km/m-1 s-2. and 850-700 mb moisture flux anomalies of 2-4+
standard deviations above the mean. There is fairly good model
agreement with heavy precip totals of 3-5" primarily over northwest
California, with isolated totals of 6-8" possible. The previous
moderate risk area was adjusted slightly southward by approximately
10-40 nm to account for model max axis consensus. Hourly rainfall
amounts of .25-.50"+ likely through the day 2 time period across
northwest CA with increasing flooding risks with time as soils
become saturated and streams and river levels rise. The HREF 1 hour probabilities for .50"+ totals for the first half of day 2 when
the data is available, remain high across northwest CA.

Oravec

Day 3
Valid 12Z Thu Nov 21 2024 - 12Z Fri Nov 221 2024

...THERE IS A HIGH RISK FOR EXCESSIVE RAINFALL ACROSS PORTIONS OF
NORTHWEST CALIFORNIA...

The deep northeast Pacific Vortex remains nearly stationary day 3
off the Pacific Northwest coast, supporting the continuation of the
multi day Atmospheric River event for northwest CA into far
southwest OR. Anomalous deep layered southwesterly flow will
continue on the south side of this vortex. 850 to 700 mb moisture
flux anomalies will continue to be 2 to 4+ standard deviations
above the mean with IVT values also maintained in the 500 to 800 km/m-1
s-2 range across northwest CA into far southwest OR. There is a
likelihood of very heavy rains again falling day 3 over similar
regions from the day 2 period. Hourly rates of .25-.50"+ likely to
continue at times supporting additional 24 hour rainfall amounts
of 3 to 6 inches and isolated additional 24 hour totals of 6-8"
across northwest CA into southwest OR. Storm total amounts of 12 to
16+ inches possible across portions of northwest California. Given
this day 2-3 heavy rain overlap potential, a small high risk area
was introduced over northwest CA, across the west central portions
of the EKA's CWA. Flood risks will continue to increase day 3 along
with rock and land slides as soils become saturated and streams
and rivers continue to rise and overflow. There will be a
northward shift back into far southwest Oregon day 3 for the heavy
rain potential as the upper flow back and heights rise. The rising
heights will also keep much of the day 3 precip as rain, increasing
overall runoff.


Oravec
$$
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FOUS30 KWBC 200809
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
309 AM EST Wed Nov 20 2024

Day 1
Valid 12Z Wed Nov 20 2024 - 12Z Thu Nov 21 2024

...THERE IS A MODERATE RISK FOR EXCESSIVE RAINFALL ACROSS PORTIONS
OF NORTHWEST CALIFORNIA...

The latest model guidance remains consistent with the overall
evolution of the strong multi day atmospheric river event into
northwest California. The low that deepened rapidly over the
northeast Pacific Tuesday, will continue to anchor deep layered
west southwest flow on the south side of this system, impacting
northwest California day 1 with IVT values of 500-800 km/m-1 s-2.
and 850-700 mb moisture flux anomalies of 2-4+ standard deviations
above the mean. There is fairly good model agreement with heavy
precip totals of 3-5" primarily over northwest California and the
northern Sierra, with isolated totals of 6-8" possible. HREF
neighborhood probabilities are very high for 5"+ amounts across
northern California, with most areas showing 80-90%+, while 8"+
probabilities are 40-80% along the northwest CA coast and 40-60%+
over the northern Sierra. Hourly rainfall amounts of .25-.50"+
likely through the day 1 time period across northwest CA with
increasing flooding risks with time as soils become saturated and
streams and river levels rise. The HREF 1 hour probabilities for
.50"+ totals remain high in the max inflow band across northwest
CA for all of day 1. This band does continue to sink south for the
first few hours of day 1, but then become nearly stationary for the
remainder of the day 1 time period. No significant change to the
previous outlook. The slight risk was extended approximately 75
miles farther south in the lee of the northern Sierra where 2-4"
rainfall totals are possible.

Oravec


Day 2
Valid 12Z Thu Nov 21 2024 - 12Z Fri Nov 22 2024

...THERE IS A HIGH RISK FOR EXCESSIVE RAINFALL ACROSS PORTIONS OF
NORTHWEST CALIFORNIA...

The strong Atmospheric river event into northwest California will
continue into day 2 as deep layered southwesterly flow continues
to the south of the northeast Pacific upper vortex. The anomalous
deep layered southwesterly flow will continue to support 850 to 700
mb moisture flux anomalies of 2 to 4+ standard deviations above
the mean and IVT values in the 500 to 800 km/m-1 s-2 range across
northwest CA. During the second half of day 2, a strong vort
rotating around the base of the northeast Pacific vortex will
support another rapidly deepening low moving northeast
approximately 200 miles off the Pacific Northwest coast. While this
second rapid cyclogenesis event will not be as strong as the
Tuesday event, it will help to begin to push the best onshore flow
axis back to the north during the second half of day 2, returning
heavy precip into southwest Oregon. There is a likelihood of very
heavy rains again falling day 2 over similar regions from the day 1
period. Hourly rates of .25-.50"+ likely to continue at times
supporting additional 24 hour rainfall amounts of 3 to 6 inches and
isolated additional 24 hour totals of 6-8" across northwest CA
into southwest OR. Storm total amounts of 12 to 16+ inches possible
across portions of northwest California. Given the 2 days of very
heavy totals in the same region, no significant changes were made
to the previous high risk area. Significant flood risks will
continue to increase day 2 along with rock and land slides as soils
become saturated and streams and rivers continue to rise and
overflow. Ahead of the next deepening low, rising heights over
northern California will keep much of the precipitation in the form
of rain. This will increase the runoff threats for areas in the
lee of the northern Sierra. Across this region, the risk area was
increased from slight to moderate from the previous issuance.


Day 3
Valid 12Z Fri Nov 22 2024 - 12Z Sat Nov 23 2024

...THERE IS A MODERATE RISK FOR EXCESSIVE RAINFALL ACROSS PORTIONS
OF NORTHWEST CALIFORNIA...

The multi day atmospheric rive event will begin to weaken on day 3
as the onshore southwesterly flow weakens and the best onshore flow
axis shifts southward. The heaviest totals day 3 likely into the
upslope of the northern Sierra where high heights will again favor
a majority of the precip falling as rain. A moderate risk was added
for this region where additional totals day 3 of 2-4 inches
possible across areas that received 5-8+ inches days 1 and 2. Along
the northwest California coast, additional heavy preip totals
likely day 3, but amounts will be much less than the day 1 and day
2 amounts, generally 1 to 1.50"+, with localized 2"+ totals. A
slight risk was maintained here given the effects from the day 1
and 2 amounts, which will support additional runoff issues for
lesser than normal amounts to produce runoff concerns.

Oravec
$$
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FOUS30 KWBC 220747
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
247 AM EST Fri Nov 22 2024

Day 1
Valid 12Z Fri Nov 22 2024 - 12Z Sat Nov 23 2024

...THERE IS A MODERATE RISK FOR EXCESSIVE RAINFALL ACROSS PORTIONS
OF NORTHERN CALIFORNIA...

The long duration, multi-day atmospheric river event that has been
impacting northern California will finally begin to become more
progressive and start to wane in intensity as a cold front just
offshore of the West Coast advances inland and drives the axis of
deeper layer Pacific moisture transport south and eastward.

However, there will still be one more day of locally very heavy
rainfall totals which are expected to be excessive and capable of
driving locally significant flooding impacts. The 00Z HREF guidance
supports some additional 5 to 10 inch rainfall totals for the
24-hour period ending 12Z/Saturday, with the heaviest totals
expected to be over the windward slopes of the northern Sierra
Nevada, and perhaps locally a few of the coastal ranges just north
of the Bay Area where there has already been very heavy rainfall
totals over the last couple of days.

IVT magnitudes along and just south of the cold front will be rather
high at the start of the period this morning, with magnitudes over
coastal areas of northwest California upwards of 750+ kg/m/s, and
these values should decrease slowly and settle southward toward
00Z. However, as the front gets into the Bay Area and the Central
Valley by early this evening, there is some suggestion in the
guidance that the front will slow down again just a bit. Coinciding
with that will be arrival of a shortwave and associated upper-
level jet streak (130+ kts) rounding the base of the deep offshore
trough. This should foster a temporary resurgence/strengthening of
the IVT values in the 00Z to 06Z time frame across the Bay Area and
extending inland across portions of the Central Valley and
foothills of the Sierra Nevada. Thus expectations are that heavy
rains will overspread all of these areas along with some localized
increase in rainfall rates this evening. In general, the rainfall
rates will be capable of reaching 0.50" to 0.75"/hour across the
coastal ranges around the Bay Area and also into the upslope areas
of the northern Sierra Nevada. Given the additional rainfall
amounts, and considering the antecedent conditions at this point,
the Moderate Risk area is maintained across the northern Sierra
Nevada, with a separate Moderate Risk introduced just north of the
Bay Area involving Sonoma and Napa Counties. Other adjustments
include extending the Marginal and Slight Risk areas a bit farther
south to include the coastal ranges a bit south of the Bay Area and
also more areas of the Central Valley. Flooding impacts will again
be rather widespread and locally significant, with additional
concerns for debris flows, rock and landslide activity, and flash
flooding involving burn scar locations. In fact, the Park Fire burn
area involving parts of Tehama and Butte Counties will need to be
very closely monitored today for enhanced impacts given the amount
of rainfall that is forecast here.

Orrison


Day 2
Valid 12Z Sat Nov 23 2024 - 12Z Sun Nov 24 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE SIERRA NEVADA...

At 12z Saturday the cold front and associated moisture plume will
be dropping south across the central Sierra Nevada. By this time
rainfall intensity will be decreasing, and the axis of better
moisture will be dropping south of the areas hardest hit over the
past few days. Thus the flood risk should be pretty low Saturday
morning along this southward dropping front.

Some weak post frontal instability is forecast which could allow for
locally heavy showers in the wake of the front over the western
slopes of the central Sierra Nevada. Not expecting anything too
intense or widespread, however there is at least a chance that a few
cells could drop a quick 0.5" or so of rain. This would be falling
over increasingly saturated ground, and so a localized flood risk is
possible. Thus we will maintain the small Marginal risk where a few
heavier post frontal showers are possible Saturday.

Chenard


Day 3
Valid 12Z Sun Nov 24 2024 - 12Z Mon Nov 25 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
NORTHWEST CALIFORNIA INTO FAR SOUTHWEST OREGON...

Locally heavy rain will be possible Sunday into Sunday night over
northwest CA into far southwest OR. A front slowing near the coast
will provide plentiful low level moisture convergence, and mid level
shortwave energy should provide some additional lift as well.
Moisture is a limiting factor for heavy rainfall with the better
moisture plume situated well south and not really getting drawn into
this system. Thus this is not expected to be a significant
atmospheric river, and normally would not expect a system of this
nature to pose a flood risk. However given the significant rainfall
over the past few days, this additional rainfall may be enough to
cause some localized additional flooding as the area will be more hydrologically sensitive than normal. Still some model differences
in the exact evolution of this system and thus rainfall amounts this
period are uncertain...but current indications suggest localized
amounts of 2-3" will be possible.

Chenard

$$
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FOUS30 KWBC 230748
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
248 AM EST Sat Nov 23 2024

Day 1
Valid 12Z Sat Nov 23 2024 - 12Z Sun Nov 24 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE SIERRA NEVADA...

A cold front and the remnants of the long duration, multi-day
atmospheric river that has been impacting the West Coast will be
dropping south across the central Sierra Nevada early this morning.
As the deeper layer moisture flux parameters/IVT magnitudes
continue to weaken and thin out, the rainfall rates will be
continuing to drop off. However, there still may be a sufficient
level of upslope flow/orographic ascent in the foothills of the
central Sierra Nevada for a few more hours early this morning of
spotty 0.25" to 0.50"/hour rainfall rates. Some weak post-frontal
instability is also still forecast which could allow for some
scattered pockets of heavy shower activity going through midday to
impact some of the western slopes of the central Sierra Nevada.
This could result in some isolated quick- hitting 0.25" to 0.50"
rainfall amounts, but these convective cells are forecast to be
progressive. Overall, the additional storm total amounts based off
the 00Z HREF guidance may reach as high as 1 to 2 inches.

Given the very wet antecedent conditions, the additional rains may
foster some additional localized runoff/flooding concerns. Thus,
the Marginal Risk area over portions of the Sierra Nevada will be
maintained.

Orrison


Day 2
Valid 12Z Sun Nov 24 2024 - 12Z Mon Nov 25 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
NORTHWEST CALIFORNIA INTO FAR SOUTHWEST OREGON...

Locally heavy rain will be possible Sunday into Sunday night over
northwest CA into far southwest OR. A front slowing near the coast
and a weak low to mid level wave riding along it will support a
modest uptick in IVT and plentiful low level convergence. Moisture
is a limiting factor for heavy rainfall with the better moisture
plume situated well south and not really getting drawn into this
system. Thus this is not expected to be a significant atmospheric
river, and normally would not expect a system of this nature to
pose a flood risk. However given the significant rainfall over the
past few days, this additional rainfall may be enough to cause some
localized additional flooding as the area will be more
hydrologically sensitive than normal.

We are still seeing some spread in model QPF output over this
period. If some of the more aggressive solutions pan out then we
could see 1-3" of rainfall is spots with hourly totals peaking
around 0.3-0.4" in the typically more favored upslope areas.

Chenard


Day 3
Valid 12Z Mon Nov 25 2024 - 12Z Tue Nov 26 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
NORTHERN CALIFORNIA INTO FAR SOUTHWEST OREGON...

Showery conditions will likely continue across portions of northern
CA and southwest OR Monday into Monday night as a deep layered low
and shortwave energy moves inland. Certainly not a classic setup
for flooding with limited moisture and dropping IVT
values...however this area remains more hydrologically sensitive
than normal following the significant atmospheric river event the
past few days. Additional rainfall over far northwest CA into
southwest OR is generally 1-3" in the guidance, with isolated
totals of this magnitude also possible over the western slopes of
the northern Sierra Nevada.

A more significant plume of moisture/IVT will actually move into
portions of southern/central CA...generally from portions of San
Luis Obispo and Monterey counties into the western slopes of the
southern Sierra Nevada. QPF has been trending up with this system,
although still seeing some model spread. The latest model consensus
suggests a possible 2-3" of rain along the coastal ranges and the
southern Sierra below snow levels. Not seeing any instability with
this system and large scale forcing is only modest, so hourly
rainfall rates are generally not expected to exceed 0.5". Given
this, and the fact that most of this area has not seen significant
rainfall recently, will continue with no areas in the excessive
rainfall outlook for now.

Chenard

$$
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FOUS30 KWBC 240816
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
316 AM EST Sun Nov 24 2024

Day 1
Valid 12Z Sun Nov 24 2024 - 12Z Mon Nov 25 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
NORTHERN CALIFORNIA INTO FAR SOUTHWEST OREGON...

Locally heavy rain will be possible today and especially tonight
over portions of northern CA into far southwest OR as an offshore
shortwave and attendant wave of low pressure arrives near the
coastal ranges. Generally the IVT magnitudes out ahead of this
surface wave will be modest with values increasing to as high as
250 to 400 kg/m/s. However, with a front nearby and favorable
upslope flow/orographic ascent involving the coastal ranges, there
will likely be some concentrations of heavier shower activity with
rainfall rates capable of occasionally reaching into the 0.25" to
0.50"/hour range. Some pockets of heavier rain may also make it
into the far northern Sacramento Valley and adjacent foothills of
the northern Sierra Nevada and Shasta/Siskiyou ranges. The 00Z HREF
guidance supports some spotty 1 to 3 inch rainfall amounts going
through early Monday morning, and thus this is not expected to be a particularly heavy event. However, given the significant rainfall
and lingering hydrological impacts from the most recent atmospheric
river, these additional rains may result in at least some
localized runoff problems and flooding.

Orrison


Day 2
Valid 12Z Mon Nov 25 2024 - 12Z Tue Nov 26 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF CALIFORNIA AND SOUTHWEST OREGON...

Showery conditions will likely continue across portions of
northern CA and southwest OR Monday into Monday night as a deep
layered low and shortwave energy moves inland. Certainly not a
classic setup for flooding with limited moisture and dropping IVT
values... however this area remains more hydrologically sensitive
than normal following the significant atmospheric river event the
past few days. Additional rainfall over far northwest CA into
southwest OR is upwards of 1-3" in the guidance, with isolated
totals of this magnitude also possible over the western slopes of
the northern Sierra Nevada.

A more significant plume of moisture/IVT will move into portions of southern/central CA...generally from portions of San Luis Obispo and
Monterey counties into the western slopes of the southern/central
Sierra Nevada. IVT values are forecast to be around 500-600 kg/ms,
which at this latitude is starting to approach climatological max
values for late November. PWs are also forecast to increase to
around the 99th percentile for late November, and thus expecting
plenty of moisture and upslope flow to allow for decent rainfall
totals. Not expecting any instability, so rainfall intensity will be
solely driven by the aforementioned moisture transport and upslope enhancement...and these factors alone are unlikely to support
rainfall rates high enough for true flash flooding. However we will
have an extended period of time with elevated IVT values, and so a
prolonged steady rainfall could eventually result in some localized
minor flood concerns. Overall expecting 1-3" of rain over the
coastal ranges in San Luis Obispo and Monterey counties (with
localized totals towards 4" possible)...with totals ranging from
near 1" in the eastern valley locations to 2-4" over the western
Sierra below snow levels.

Chenard


Day 3
Valid 12Z Tue Nov 26 2024 - 12Z Wed Nov 27 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE CENTRAL AND SOUTHERN SIERRA NEVADA...

The atmospheric river event described in the day 2 discussion
continues into Tuesday over portions of the central and southern
Sierra Nevada. There is a bit more model spread by this time with
regards to the persistence of the IVT and strength of the mid/upper
forcing. A majority of the 00z deterministic models have trended a
bit weaker and faster with the shortwave energy pushing across CA
and into NV...and this trend would result in less additional QPF
over central CA on day 3. However the 00z GEFS and recent NBM
probabilities suggest there is still a chance for a slower/stronger
wave resulting in more robust rainfall amounts.

This will be the 2nd consecutive day of steady rainfall for these
areas, and so do expect some increased hydrologic sensitivity that
could result in at least some localized minor flooding issues. When
summing the two days of rainfall together, the latest WPC
deterministic QPF is calling for around 2" in Fresno to Visalia,
increasing to 3-6" in the foothills/western slopes of the southern
and central Sierra Nevada. Given the magnitude of IVT forecast even
even forecasting 1-2" spilling over to the east of the crest towards
Bishop and Independence. These forecast values average around a 2yr
ARI for 48 hr amounts, also supportive of a localized minor flood
threat. As mentioned above, there is both higher and lower end
potential with this forecast rainfall. The higher end scenarios
could even result in Slight risk level impacts, while the lower end
outcomes would be a minimal flood threat. So will need to continue
to monitor trends, and for now still think the Marginal risk is
appropriate.

Chenard

$$
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FOUS30 KWBC 250757
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
257 AM EST Mon Nov 25 2024

Day 1
Valid 12Z Mon Nov 25 2024 - 12Z Tue Nov 26 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE SOUTHERN SIERRA NEVADA...

Moderate to locally heavy showers are expected to continue across
portions of northern CA and southwest OR today and tonight as a
deep layered low and associated shortwave energy moves inland. The
deep layer cyclonic flow coupled some steepening of the mid-level
lapse rates and orographic ascent/upslope flow over the coastal
ranges should favor some occasional 0.25" to 0.50"/hour rainfall
rates. Some of these heavier showers will also spread inland
across the northern Sierra Nevada. Overall, the additional rainfall
amounts here should be relatively modest, but portions of the
coastal ranges of northwest CA and far southwest OR may see some
1-3" rainfall totals going through early Tuesday morning. Given the wet/saturated soil conditions and high streamflows, these
additional rains may foster some renewed runoff problems and
localized flooding. A Marginal Risk will be maintained for these
areas.

Farther south into the upslope areas of the central and especially
southern Sierra Nevada, and also the coastal ranges of Monterey,
San Luis Obispo and Santa Barbara Counties, a moderately strong
atmospheric river event will be arriving today and continuing
through tonight and early Tuesday. This will be associated with the
arrival of a southern stream shortwave impulse which will be
embedded within the transport of deeper layer subtropical moisture
extending well offshore of southern CA and upstream over the
eastern Pacific. The GFS and ECMWF support increasing IVT
magnitudes especially by 00Z across the coastal ranges and into
higher terrain of the southern Sierra Nevada with magnitudes rising
to 500 to 700+ kg/m/s. The orientation of this will be generally
orthogonal to the terrain, and this should yield enhanced
orographic ascent that will be conducive for heavier rainfall
rates.

The 00Z HREF guidance favors some occasional 0.50"+/hour rainfall
rates with the higher probabilities of this focused over the
foothills of the Sierra Nevada involving Fresno and Tulare
Counties, and a small portion of northern Kern County. A consensus
of the 00Z HREF guidance supports 24-hour rainfall totals
(generally below 9000 feet/snow level) of 3 to 6 inches, with a
couple of models indicating some spotty 6 to 8+ inch amounts.
Meanwhile, over the coastal ranges from Monterey County down
through San Luis Obispo and Santa Barbara Counties, some 1 to 3+
inch rainfall totals are supported in the guidance. One key factor
in general that is supporting these higher rainfall totals, aside
from the upslope flow into the terrain, is the fact that much of
the moisture will be of subtropical origins, and this will yield PW
anomalies as high as 2 to 4 standard deviations above normal for
this time of the year. Given the forecast rainfall amounts and
associated rainfall rates, there may be some flooding concerns that materialize, and this will include at least a localized threat for
some burn scar flash flooding/debris flow impacts. As a result, a
Slight Risk for excessive rainfall has been introduced for portions
of the southern Sierra Nevada, with some localized expansion of
the prior Marginal Risk area to account for rainfall over the
coastal ranges and parts of the San Joaquin Valley.

Orrison


Day 2
Valid 12Z Tue Nov 26 2024 - 12Z Wed Nov 27 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE CENTRAL AND SOUTHERN SIERRA NEVADA...

Model differences remain in the 25/00Z guidance with respect to
the timing of a shortwave moving inland from the California/Oregon
border with the ECMWF being faster to bring the shortwave trough
across the Sierra Nevada range and into the Great Basin by
27/00Z...although most of the 00Z suite of guidance...including the GFS...trended trended faster and a bit weaker. With the exception
of the Canadian GEM and Regional...the 25/00Z GFS remained heaviest
across the central and southern Sierra Nevada for the 24 hour
period ending Wednesday morning. Still expect some increased
hydrologic sensitivity that could result in at least some localized
minor flooding issues given that this will be the second
consecutive day of steady rainfall for these areas. Even though the
non-25/00Z GFS/Canadian consensus is for 2 to 4 inches across the central/southern Sierra Nevada over the 24 hour period, the amounts
tend to be more in the 1 to 3 inch range below the expected snow
levels (approx 9000 ft per the WPC Winter Weather Desk forecaster)
which may mitigate some of the concern for flooding. Even so...the
concern remains that those values may be too low at least locally
considering the coarser resolution of the available guidance at
longer lead times so an upgrade may still be needed later. Rainfall
rates and areal coverage of rainfall should decrease late in the
period as the flow of moisture becomes disrupted and the better
dynamics pull away from the area.

Bann


Day 3
Valid 12Z Wed Nov 27 2024 - 12Z Thu Nov 28 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Bann
$$
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FOUS30 KWBC 020710
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
210 AM EST Mon Dec 2 2024

Day 1
Valid 12Z Mon Dec 02 2024 - 12Z Tue Dec 03 2024

Onshore flow across far south Texas will maintain a moist/unstable
airmass that could conditionally support heavy rainfall near the
Brownsville vicinity and adjacent coastal areas especially from the
afternoon onward. This risk is too isolated/conditional for
inclusion of a Marginal risk area at this time but will be
monitored through the day. The probability of rainfall exceeding
flash flood guidance is less than 5 percent.

Cook


Day 2
Valid 12Z Tue Dec 03 2024 - 12Z Wed Dec 04 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Wegman


Day 3
Valid 12Z Wed Dec 04 2024 - 12Z Thu Dec 05 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

The Marginal Risk area for portions of eastern Texas and much of
western Louisiana that was inherited was removed with this update.
A fairly robust 30-40 kt LLJ will advect Gulf moisture into much of
the Mississippi Delta region and west into eastern Texas on
Wednesday. PWATs may exceed 1.75 inches, especially along the Gulf
coast. However, this is the only ingredient that is sufficient for
flooding rains. Instability, while non-zero...will be meager,
struggling in most areas to get to 500 J/kg of MUCAPE. This will be
the primary limiting factor against flooding, as a lack of
instability should keep most of the rain as stratiform. Secondly,
much of the eastern half of the U.S., including eastern Texas and
Louisiana have been very dry lately, so stream and creekbeds are
running low. The drawn out period of mostly light rain in this
area will therefore mostly be beneficial. While embedded convective
cells could briefly cause locally heavy rain, the dry conditions
and high FFGs should mitigate any flooding. Finally, at the tail
end of the event late Wednesday night into Thursday, cold frontal
passage will push any heavy rain south and out of where the
heaviest rains are expected over central Louisiana. This too should
diminish the flooding potential.

As always, increases in the guidance for rainfall amounts in the
next couple days or greater instability could require a reissuance
of the Marginal, but for now the rainfall in the guidance likely
falls in the sub-Marginal 0-5% chance category area-wide.

Wegman

$$
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FOUS30 KWBC 030729
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
229 AM EST Tue Dec 3 2024

Day 1
Valid 12Z Tue Dec 03 2024 - 12Z Wed Dec 04 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF SOUTH TEXAS...

A moist airmass (characterized by 1.4+ inch PW values) will migrate
slowly northwestward through the day along a surface trough located
near the south Texas coast. Convergence along that trough axis
will support areas of deep convection through the day, with
kinematic profiles supporting slow storm motions even as mid-level
flow weakens during the forecast period. Isolated spots of 2-4 inch
rainfall amounts appear possible per latest CAMS in the Marginal
Risk area. Isolated flash flood potential will exist in this
regime.

Cook


Day 2
Valid 12Z Wed Dec 04 2024 - 12Z Thu Dec 05 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Wegman


Day 3
Valid 12Z Thu Dec 05 2024 - 12Z Fri Dec 06 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Wegman
$$
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FOUS30 KWBC 040721
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
221 AM EST Wed Dec 4 2024

Day 1
Valid 12Z Wed Dec 04 2024 - 12Z Thu Dec 05 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent. Strengthening warm/moist advection across east Texas
and Louisiana will result in widespread shower and thunderstorm
activity most of the day through early Thursday. Several areas of
2-4 inch rainfall totals are expected especially from southeast
Texas into central Louisiana. The rain will fall in areas that have
not experienced appreciable rainfall over at least the past week,
and models are inconsistent with depiction of any focused corridors
of heavier and/or training convection that could result in larger-
scale flash flood concerns. FFG thresholds are also relatively
high. <5% probabilities are maintained for this outlook with the
expectation that any flash flood concerns should be isolated at
best.

Cook


Day 2
Valid 12Z Thu Dec 05 2024 - 12Z Fri Dec 06 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Wegman


Day 3
Valid 12Z Fri Dec 06 2024 - 12Z Sat Dec 07 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Wegman
$$
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FOUS30 KWBC 050738
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
238 AM EST Thu Dec 5 2024

Day 1
Valid 12Z Thu Dec 05 2024 - 12Z Fri Dec 06 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Otto


Day 2
Valid 12Z Fri Dec 06 2024 - 12Z Sat Dec 07 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Wegman


Day 3
Valid 12Z Sat Dec 07 2024 - 12Z Sun Dec 08 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR MUCH OF
EASTERN TEXAS...

A low-level jet streaming Gulf moisture northward across eastern
Texas will interact with a strong shortwave trough which will move northeastward out of New Mexico and into the central Plains. PWATs
along the upper Texas coast are expected to increase to above 1.75
inches by Saturday night. While shower and light rain activity is
expected especially over western portions of the Marginal Risk area
during the day Saturday, the heaviest rain will be on Saturday
night due to the typical nocturnal strengthening of the LLJ.
Instability will be the primary limiting factor as MUCAPE values
struggle to even get above a couple hundred J/kg. Portions of the
Marginal Risk area will get some rain Friday and Friday night, such
that this much stronger second round may train over some areas
that due to previous rain may have more saturated soils. Isolated
flash flooding is possible, especially in urban and flood prone and
low lying areas.

Wegman

$$
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FOUS30 KWBC 061533
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1033 AM EST Fri Dec 6 2024

Day 1
Valid 12Z Fri Dec 06 2024 - 12Z Sat Dec 07 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

...Far Deep South Texas...
The slow sagging frontal zone is nearly flat west to east across
the Northern Gulf of Mexico and a weak surface to boundary layer
cyclone has developed along the upstream edge near the southern tip
of Texas. Enhanced deep layer moisture resides along and north of
the boundary across this section of the front with total PWat
values ranging from 1.5-1.75". Warm sea surface and proximity to
the front allow for some weak instability in proximity to that low
with values of 750-1000 J/kg available along/offshore. So there
will remain some solid potential for thunderstorm activity across
far south Texas. However, the vast majority of guidance continues
to suggest best overall convergence and strongest updrafts will
remain offshore or at the near coast. It is possible some weakening
showers or rouge thunderstorm may make an appearance onshore in
proximity to the urban corridor of the lower Rio Grande Valley,
making the risk for flash flooding non-zero, but not rising to high
enough probability/coverage to reach 5% threshold for delineating
a Marginal Risk at this time.

Gallina


Day 2
Valid 12Z Sat Dec 07 2024 - 12Z Sun Dec 08 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
EASTERN TEXAS AND WESTERN LOUISIANA...

A low-level jet streaming Gulf moisture northward across eastern
Texas will interact with a strong shortwave trough which will move northeastward out of New Mexico and into the central Plains. PWATs
along the Upper Texas coast are expected to increase to 1.5"+ and
instability should remain minimal (and mostly confined to the
coast). The heaviest rain is forecast to be on Saturday night due
to the typical nocturnal strengthening of the low-level jet. Soils
have become a bit more saturated in this region due to the recent
rainfall, and some rainfall is expected on Friday. Isolated flash
flooding is possible, especially in areas of more saturated soils,
urban areas, and flood prone/low lying areas.

Churchill/Roth


Day 3
Valid 12Z Sun Dec 08 2024 - 12Z Mon Dec 09 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
LOWER MISSISSIPPI VALLEY AND CENTRAL GULF COAST...

Continued moisture flux transport via a moderately strong low-
level jet is expected to result in increasing coverage of flash
flooding on Sunday, as the bulk of the forcing and jet dynamics
via the aforementioned strong shortwave trough will not arrive
until midday (along with maximized instability). Localized training
is expected to result in 2-4" totals, suggesting a lower-end
Slight Risk based on the probability spectrum (which ranges from
15-40%). Given that most of the region is experiencing very dry
antecedent soil conditions (10th percentile or lower for much of
MS/AR/LA, per NASA SPoRT-LIS 0-100 cm soil moisture), any flooding
should be relegated to flood-prone areas (with the greatest risk
for any localized significant flash flooding over west-central LA,
where antecedent soil conditions and streamflows are locally higher).


Churchill
$$

d
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FOUS30 KWBC 070820
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
320 AM EST Sat Dec 7 2024

Day 1
Valid 12Z Sat Dec 07 2024 - 12Z Sun Dec 08 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Churchill


Day 2
Valid 12Z Sun Dec 08 2024 - 12Z Mon Dec 09 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE CENTRAL GULF COAST...

The Slight Risk has been maintained along and near the central
Gulf Coast for Sunday and Sunday night, confined to where more
appreciable deep-layer instability exists to support a higher
probability of more intense short-term rainfall rates (2"+/hr).
Still, this is considered a lower-end Slight Risk (based on the
wide 15-40% probability spectrum), suggesting widely scattered
instances of flash flooding at best (given expected localized
totals of 2-4" are near the corresponding 3-hr FFGs of 3-4").
Also, much of the Slight Risk area, particularly from Jasper TX
east-northeast to Alexandria LA, have received heavy rainfall over
recent days, and as a result the antecedent soil conditions and
streamflows are a bit higher compared to areas farther north (where
NASA SPoRT-LIS 0-100 cm soil moisture in the bottom 10th percentile
for much of MS/AR/LA). In addition to drier antecedent conditions
farther north and east across the Mid-South, very limited elevated
instability (MU CAPE ~200 J/kg at best) should prevent rainfall
rates from climbing too high (generally 1.5"/hr or less, driven by
impressive forcing via the shortwave and associated jet dynamics).
This suggests that a Marginal Risk should suffice with any flash
flooding being highly localized, despite areal average rainfall
amounts near 2" (expected to be spread out over 6+ hours).

Churchill/Hurley


Day 3
Valid 12Z Mon Dec 09 2024 - 12Z Tue Dec 10 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
CENTRAL GULF COAST...

The shortwave trough responsible for heavy rainfall on Sunday over
much of the Lower MS Valley looks to eject northeastward into the
central Appalachians and Mid-Atlantic on Monday, bringing largely
beneficial rainfall (with totals generally under 1") to much of the
Northeast. Farther south along the central Gulf Coast, there are
hints of another (weaker) shortwave trough within the southern
stream that may enhance heavy rainfall along a trailing cold front.
Given the slowing of the front, the opportunity for training areas
of heavy rainfall will be greater on Day 3, best depicted by the
00z ECMWF and ECENS (depicting localized banded totals of 2-5" and probabilities for 2" exceedance as high as 30%). This risk appears
greatest from southeast LA to southern AL and the tip of the FL
Panhandle, though the EC model system is the most extreme and
farthest east of all the models. Maintained the inherited Slight
Risk area with some adjustments, limiting the eastern extent a bit
given the lack of agreement from the other models. Uncertainty is
still relatively high, but subsequent outlooks should get a better
handle on things as these details begin to enter the CAM period.

Churchill
$$
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FOUS30 KWBC 080805
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
305 AM EST Sun Dec 8 2024

Day 1
Valid 12Z Sun Dec 08 2024 - 12Z Mon Dec 09 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR MUCH OF THE
LOWER MISSISSIPPI VALLEY...

The inherited Marginal Risk area was maintained for this update,
suggesting that any flash flooding should remain localized today,
as rainfall rates will generally remain capped below 1"/hr (with
lacking instability being the primary limiting factor). The
heaviest rains for the period are expected in the middle of the
Marginal Risk area over northern Mississippi, where an interaction
with a front in that area will lead to greater forcing than areas
farther south along the Gulf Coast. Where the front adds additional
forcing, localized convective bursts may be embedded within the
broader rainfall shield.

Hydrologically, most if not all of the soils in the are are at or
below average for moisture. Low/dry creek beds should easily
handle most of the light to briefly moderate rainfall rates. Any
isolated flooding will be in any urban areas, as well as other low-
lying or more flood-prone areas.

Churchill/Wegman


Day 2
Valid 12Z Mon Dec 09 2024 - 12Z Tue Dec 10 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
EASTERN LOUISIANA AND COASTAL MISSISSIPPI...

The shortwave trough responsible for heavy rainfall on Sunday over
much of the Lower MS Valley looks to eject northeastward into the
central Appalachians and Mid-Atlantic on Monday, bringing largely
beneficial rainfall (with totals generally well under 1") to much
of the Northeast. Farther south along the central Gulf Coast, a
weaker shortwave within the southern stream may locally enhance
heavy rainfall along a trailing cold front. The inherited Slight
Risk in this area was maintained, mainly from the I-10 & I-12
corridors from Baton Rouge east to Biloxi, where the flooding
potential appears greatest in urban and more flood-prone areas
(given relatively dry antecedent conditions and streamflows normal
to below normal). There is still some question as to how far east
the heavy rainfall threat will extend (as the ECMWF and ECENS have
been persistent outliers suggesting an eastward extension into the
FL Panhandle and surrounding southeast AL and southwest GA), but
the signal for localized totals of 2"+ are maximized near the
Slight Risk (and confined to where instability and forcing are
greatest).

Churchill


Day 3
Valid 12Z Tue Dec 10 2024 - 12Z Wed Dec 11 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
SOUTHEAST AND CENTRAL GULF COAST...

Large scale upper trough will be digging into the central US by
Tuesday, setting the stage for more organized heavy rainfall into
portions of the Southeast. Initially positively tilted, the trough
looks to quickly take on a more neutral tilt over the course of
the course of the day, as an associated 250 mb jet streak
strengthens from ~110 kts to ~170 kts over 24 hours (with our area
of interest for the Slight Risk located near the right-entrance
region). As with prior days, instability once again looks to be the
primary limiting factor, and this is particularly the case farther
north into the Carolinas. While the GFS/GEFS depict 2-4" localized
totals into northern GA and western SC, the ECMWF/ECENS largely
limit this threat (for 2" and 3" exceedance) a bit farther south
into central GA, southeast AL, and the FL Panhandle (where the
inherited Slight Risk was maintained and adjusted a bit based on
the new model data). Given relatively dry antecedent conditions and
associated 3-6 hr FFGs generally ranging from 3.0-4.0", the Slight
is on the lower-end of the 15-40% probability distribution,
suggesting widely scattered instances of flooding (at best).

Churchill

$$
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FOUS30 KWBC 090758
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
258 AM EST Mon Dec 9 2024

Day 1
Valid 12Z Mon Dec 09 2024 - 12Z Tue Dec 10 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE CENTRAL GULF COAST...

Overall pattern evolution will continue to point to a benign
instability axis (MUCAPE ~500-1000 J/kg) being confined closer to
the Gulf with sufficient deep layer shear and moisture presence
(PWATs b/w +1 to +2 deviations) allowing for a small area of
convective development capable of locally enhanced rainfall rates
for flash flood potential. Given the overall antecedent dry
conditions prior, the prospects of flash flooding will likely be
relegated to more urban settings along the Central Gulf coast,
including places such as New Orleans, Biloxi, and Mobile. A few
other Parishes within Southeastern LA also contain areas that
experience a bit easier ability to flash flood given some of the
above urbanization factors, so decided to maintain the previous
SLGT risk inheritance with only some minor modifications made to
the overall risk area.

Latest 00z HREF neighborhood probabilities for >3" of rainfall are
within the low-end 20-25% range with highest prospects likely
between 1-2" when taking relevant CAMs into account. This is
similar to the previous forecast prob fields from the 12z HREF
iteration, and with coordination from the local WFOs along the Gulf
Coast earlier for the SLGT risk, there was no need to deviate from
what was proposed in the last update. Best chance will reside from
training echoes on persistent west-southwest flow during the
diurnal instability maximum, carrying into the evening before the
setup decays prior to the next period of relevant convection for
D2.

Kleebauer


Day 2
Valid 12Z Tue Dec 10 2024 - 12Z Wed Dec 11 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM SOUTHEASTERN
ALABAMA TO UPSTATE SOUTH CAROLINA...

As the previous shortwave trough kicks to the northeast, a stronger
mid-level trough will dig quickly out of the Rockies into the
Southern Plains by Tuesday morning with sights downstream on areas
east of the Mississippi. Increasing meridional flow ahead of the
digging trough will aid in the advection of deep moisture poleward
with the initial surge propagating north out of the Gulf through
the Southeast by Tuesday afternoon, eventually spreading northward
into the Southern and Central Mid Atlantic the second half of the
period. The advection pattern will be sufficient in increasing
regional mid-level instability as profile moisture saturates deeper
into the profile across the areas above. PWAT anomalies on the
order of 2-3 deviations above normal will be common over parts of
GA spreading up through the neighboring Carolinas, eventually
surging into the Central Mid Atlantic and Northeastern U.S by the
end of the D2 cycle. This will prime several areas for heavy
rainfall prospects as the final ingredients come to together for a
locally enhanced precip pattern.

The trough to the west will begin tilting more neutral with a
strengthening upper jet positioning allowing for large scale ascent
to increase in earnest as we move into Tuesday afternoon and
beyond. The main trigger for a line of enhanced convection will
form at the hands of a strong surface cold front that will shove
eastward beneath an intensifying surface low that develops in
conjunction to the favorable upper level evolution. Current
deterministic sfc to 850mb wind field indicates a corridor of
backed flow across much of GA into the Carolinas during Tuesday
evening ahead of the cold front allowing for widespread rainfall to
develop downstream of the approaching front. As the cold front
swings eastward by late Tuesday night through early Wednesday, the
peak rainfall rates will be occurring across the Carolina Piedmont
down through Central GA, aligning with the cold front as it moves
through the region. The eventual heavy rain footprint will spread
northeastward into the Southern Mid Atlantic with locally heavy
rainfall impacting areas as far north as Virginia with some lighter
precip making headway into areas further north. Places across
Southwestern VA down to the I-40 corridor in NC will see anywhere
from 1-2" of rainfall with locally higher further south through the
zone. 2-3" with local totals to 4" will be plausible for the area
extending from Southeastern AL through Central GA into Upstate SC,
an area more prone to flash flood prospects thanks to the
complexity of the local terrain.

This signal has been prevalent over the past series of
deterministic model outputs and is now firmly within the ensemble
mean as bias corrected ENS now supports 2.5-3" through much of the
area outlined above in the 2-3" forecast. The saving grace in this
setup is the time of year allowing for lower surface based
instability parameters and very dry antecedent conditions leading
into the event. This allowed for a SLGT risk to be sufficient for
the setup, a carry over from the previous forecast. The MRGL risk
still extends into VA where the northern periphery of the heavy
rainfall is expected.

Kleebauer


Day 3
Valid 12Z Wed Dec 11 2024 - 12Z Thu Dec 12 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM CENTRAL AND
EASTERN LONG ISLAND UP THROUGH MUCH OF NEW ENGLAND...

As the longwave pattern evolves further, the neutral-tilted trough
from previous D2 time frame will enhance further with the mean
trough taking on a more negative tilt allowing for enhanced surface
low strengthening as the surface low progresses northward into New
England and eventually Quebec. PWAT anomalies on the order of 2-3
deviations above normal will quickly progress northward
encompassing much of New England by Wednesday afternoon, even
getting up towards +4 deviations as we move into Wednesday night
over Northern New England from NH through ME. This pattern is
textbook for a corridor of heavy rainfall to spread from the Mid
Atlantic through all of the Northeast with the primary areas of
interest location along and ahead of the cold front that will sweep
eastward during the forecast period. Portions of Western NY state
and Northern PA will eventually change to winter precipitation
allowing for a decay in flash flood concerns, however areas
downstream will be under a respectable deluge of rainfall prior to
the rain threat ceasing in wake of the front.

Totals of 1.5-2.5" of rain are forecast across much of Long Island
up through Southern New England, eventually moving up through ME
as we close out the forecast period. 1-2" is forecast for points
further west, but those areas also have the added snow melt factors
that will play into the flooding concerns as high dewpoints and
heavy rain will promote rapid snow melt for places in the interior
over VT/NH and the neighboring Berkshires in MA. The expectations
are for some creeks and smaller streams to become problematic in
the setup and could cause localized flood concerns during the peak
of the heavy rainfall. The rivers across New England can thankfully
take a decent surge of moisture after a very dry fall, so the
prospects of significant flooding are very low at this point.

The setup is still worthy of a large SLGT risk encompassing much
of New England with the best threats likely over urbanized areas in
LI and Southern New England and over those zones in the interior
where rapid snow melt has historical precedence for localized
flash flood concerns. A MRGL risk will encompass the SLGT risk
across Northeast with an extension down into Central and Eastern NC
as the early portion of the forecast period will still see
moderate to heavy rainfall Wednesday morning before pulling
northward.

Kleebauer
$$
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FOUS30 KWBC 100756
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
256 AM EST Tue Dec 10 2024

Day 1
Valid 12Z Tue Dec 10 2024 - 12Z Wed Dec 11 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM CENTRAL ALABAMA
THROUGH PORTIONS OF THE WESTERN CAROLINAS...

The overall synoptic pattern remains on track to deliver a swath of
heavier rainfall to portions of the Southeast and Southern Mid
Atlantic during the period. A strong mid- level trough is currently
analyzed over the Four Corners region, digging quickly to the
southeast with sights on the Southern Plains by later this morning.
As the mean trough pivots across the Southern Plains near OK/TX,
increasing meridional flow ahead of the digging trough will aid in
the advection of deep moisture poleward with the initial surge
propagating north out of the Gulf through the Southeast by the
afternoon, eventually spreading northward into the Southern and
Central Mid Atlantic the second half of the period. The advection
pattern will be sufficient in increasing regional mid- level
instability as moisture saturates deeper into the profile across
the areas above. PWAT anomalies on the order of 2-3 deviations
above normal will be common over parts of GA spreading up through
the neighboring Carolinas, eventually surging into the Central Mid
Atlantic and Northeastern U.S by the end of the D1 cycle. This
will prime several areas for heavy rainfall prospects as the final
ingredients come to together for a locally enhanced precip pattern.

The trough to the west will begin tilting more neutral with a
strengthening upper jet positioning allowing for large scale ascent
to increase in earnest as we move into the afternoon hours and
beyond. The main trigger for a line of enhanced convection will
form at the hands of a strong surface cold front that will shove
eastward beneath an intensifying surface low that develops in
conjunction to the favorable upper level evolution. Current
deterministic sfc to 850mb wind field indicates a corridor of
backed flow across much of GA into the Carolinas during Tuesday
evening ahead of the cold front allowing for widespread rainfall to
develop downstream of the approaching front. As the cold front
swings eastward by late Tuesday night through early Wednesday, the
peak rainfall rates will be occurring across the Carolina Piedmont
down through central GA into portions of east-central AL, aligning
with the cold front as it moves through the region. The eventual
heavy rain footprint will spread northeastward into the Southern
Mid Atlantic with locally heavy rainfall impacting areas as far
north as southwestern Virginia with some lighter precip making
headway into areas further north.

Recent 00z HREF output remains steadfast with the prospects of a
widespread 1-3" of rainfall across a large chunk of the Southeast
into the Highlands of the Western Carolinas with the northern
extension of any maxima peeking into southwestern Virginia where
some of the terrain will make use of the southeasterly upslope
component to the wind field. Probability fields in both the
neighborhood and EAS realm are pretty solid when it comes to the
potential with the latter of which indicating a well-defined axis
of 30-50% for at least 2", a signal prevalent historically for
favored SLGT risks or higher for the current impact areas.
Neighborhood probabilities are of course higher in percentile given
how the prob field is calculated, however the most notable output
is the very high 60-80% coverage for >3" and low-end probs of
20-25% for up to 5" across the area southeast of Birmingham up
through the Atlanta metro. This was a small shift northward in
terms of the heaviest QPF axis from previous forecasts and align
well with the latest ECMWF and GFS ML outputs, a testament to
increasing agreement within the deterministic on where the heaviest
rainfall will occur. The saving grace from this setup being a more
prolific outcome is the lack of sufficient surface based
instability that tends to add a greater convective element to the
rainfall rates that shift the signal to a higher-end risk threat.
Thankfully, that is not the case here, so the threat does remain a
bit capped on the upper bound of potential.

The previous SLGT risk was adjusted a bit further northwest across
AL/GA to reflect the change within the axis of heaviest rainfall
putting the Atlanta metro squarely within the SLGT risk forecast.
The SLGT remains firmly in-place across Upstate SC with a general
northward extension into the Appalachian front of southwestern NC
as well as small eastward expansion into the Charlotte metro to
atone for the higher QPF being signaled as of the latest 00z
guidance (All in coordination with the local WFO in
Greenville/Spartanburg). The MRGL risk remains generally in a
similar place compared to previous forecast, but some minor
adjustments to the northwest across AL and northward a bit further
into western VA with the most notable inclusion of the Birmingham
metro where the urban flash flood threat will lie right on the edge
where guidance is depicting the heaviest rainfall.

Kleebauer


Day 2
Valid 12Z Wed Dec 11 2024 - 12Z Thu Dec 12 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM CENTRAL AND
EASTERN LONG ISLAND UP THROUGH MUCH OF NEW ENGLAND...

The previous forecast remains largely unchanged as the synoptic
regime anticipated for mid-week continues to trend favorable for
heavy rainfall across much of the Northeast and Mid Atlantic. The
neutral- tilted trough from previous D1 time frame will enhance
further with the mean trough taking on a more negative tilt
allowing for enhanced surface low strengthening as the surface low
progresses northward into New England and eventually Quebec. PWAT
anomalies on the order of 2-3 deviations above normal will quickly
progress northward encompassing much of New England by Wednesday
afternoon, even getting up towards +4 to +5 deviations as we move
into Wednesday night over Northern New England from NH through ME.
This pattern is textbook for a corridor of heavy rainfall to spread
from the Mid Atlantic through all of the Northeast with the
primary areas of interest located along and ahead of the cold front
that will sweep eastward during the forecast period. Portions of
Western NY state and Northern PA will eventually change to winter
precipitation allowing for a decay in flash flood concerns, however
areas downstream will be under a respectable deluge of rainfall
prior to the rain threat ceasing in wake of the front.

Totals of 2-3.5" of rain are forecast across much of Long Island
up through Southern New England, eventually moving up through ME as
we close out the forecast period. 1-2" with locally higher amounts
are forecast for points further west, but those areas also have
the added snow melt factors that will play into the flooding
concerns as high dewpoints and heavy rain will promote rapid snow
melt for places in the interior over VT/NH and the neighboring
Berkshires in MA. The expectations are for some creeks and smaller
streams to become problematic in the setup and could cause
localized flood concerns during the peak of the heavy rainfall. The
rivers across New England can thankfully take a decent surge of
moisture after a very dry fall, so the prospects of significant
flooding are lower than normal at this point.

The previously inherited forecast was largely unchanged as the
setup and subsequent forecast is still worthy of a large SLGT risk
encompassing much of New England with the best threats likely over
urbanized areas in LI and Southern New England and over those
zones in the interior where rapid snow melt has historical
precedence for localized flash flood concerns. A MRGL risk will
encompass the SLGT risk across Northeast with an extension down
into Central and Northeastern NC as the early portion of the
forecast period will still see moderate to heavy rainfall Wednesday
morning before pulling northward.

Kleebauer


Day 3
Valid 12Z Thu Dec 12 2024 - 12Z Fri Dec 13 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Kleebauer
$$
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FOUS30 KWBC 110803
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
303 AM EST Wed Dec 11 2024

Day 1
Valid 12Z Wed Dec 11 2024 - 12Z Thu Dec 12 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM CENTRAL AND
EASTERN LONG ISLAND UP THROUGH MUCH OF NEW ENGLAND...

Potent longwave trough is currently aligned over the Mississippi
Valley with a tilt closer to neutral as of the latest UA analysis.
A vigorous 160kt speed max at 250mb was analyzed over the Ohio
Valley on the leading side of the trough with sampled winds from
the 00z KILN sounding indicating those 160kt winds are verified.
This signals a very potent upper level evolution with an
anticipated holding of strength the next few hrs before a further
strengthening is anticipated later this morning and afternoon as
the trough axis begins tilting more negative allowing for a jet
buckling downstream as the speed max enters New England and
Quebec. At the surface, multiple waves of low pressure are centered
north to south from the eastern Great Lakes, down through the
Southern Appalachians as they lie within the elongated cold front
extending down from the northern low to the Central Gulf coast. The
forecast is for these waves of low pressure to propagate northward
during the next 3-6 hrs before the surface low over the lakes
becomes the dominant SLP feature, strengthening rapidly as the
trough buckles and the low pressure centered gets positioned firmly
within the right entrance region of the very powerful jet over
northeast North America.

The evolution above will lead to a large swath of rainfall to
encompass much of the area along and east of the Appalachian front
with a trailing axis of convection situated over the southern half
of the Carolinas down into FL as the precip aligns along and just
ahead of the surface cold front. Frontal progression will lead to
rainfall shifting eastward overtime, however the environment ahead
of the front will be significantly enhanced with deep layer
moisture advecting poleward well ahead of the mean trough. PWAT
anomalies are already over +2 deviations across a good portion of
the Northeast U.S down through the Southeast with anomalies
expected to climb closer to +3/+4 deviations as me move into the
late-morning afternoon hours over the Northern Mid Atlantic into
New England. Assessment of local bufr soundings across Southern New
England from Central LI up through CT/MA/NH/ME signal a deep, uni-
directional wind field with modest theta_E advection occurring
during the morning and afternoon time frame as the warm-conveyor
points directly through the area with a well-defined warm front
bisecting the area by 18z.

The time frame between 18-00z will be the most significant time
frame with regards to heavy rainfall potential across much of New
England as the cold front begins racing eastward and the warm front
tilts southwest to northeast from Western CT up through Southern
ME. This alignment will become a focus of a strong, cold rain band
that is textbook in these evolving inland synoptic pressure falls
leading to a period where rainfall rates will be a solid 0.5-1"/hr
extending within that convergence zone. The line will advance
eastward eventually as the cold front approaches and kicks the
convergence axis downstream leading to the heavy rain threat
shifting more towards the coastal regions with sights on Eastern
MA/NH/ME towards the 00-03z time frame. Backed flow off the
Atlantic will aid in maintaining the convergent field along and
ahead of the advancing front with heavy rains lingering until the
front back finally pass through and the winds shift west to
northwesterly ushering in colder air and stabilizing the mid-levels
enough to limit the heavier precip. Prior to this occurring, a
solid 2-3" with locally as high as 4" of rainfall are anticipated
in the zone encompassing Central and Eastern LI, much of MA/NH and
the western half of ME. Rapid snow melt will be a problem for
areas located in the Northern Berkshires and Worcester Hills
towards the MA/NH border extending northward as NOHRSC snow depth
analysis pins a solid 2-4+" on the ground currently within those
zones with over a foot in parts of NH/VT/Western ME. This will
allow for potential small stream cresting and ice jam concerns in
the interior that would exacerbate flood concerns during the
heaviest of the precip time frame later this afternoon.

An expanse of Flood Watches are positioned across much of the
above areas, including all of VT as complex terrain and higher snow
depths in the Green Mountains and surrounds leading to higher than
normal flood potential, despite the heaviest rain footprint likely
a bit further east. Considering the above variables and in
coordination with local WFOs, the inherited SLGT risk was
relatively unchanged with the only shift being an extension a bit
further southwest into CT to cover for urban flood concerns within
the axis of expected heavy rainfall during the cold frontal band
being forecasted across much of the 00z CAMs suite. The MRGL risk
still extends around the SLGT and further south into the Central
Mid Atlantic and Carolinas with the primary concerns likely
isolated urban flood potential, especially in the larger metro
corridors like Raleigh, DC/Balt, and Philadelphia.

Kleebauer


Day 2
Valid 12Z Thu Dec 12 2024 - 12Z Fri Dec 13 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Kleebauer


Day 3
Valid 12Z Fri Dec 13 2024 - 12Z Sat Dec 14 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF NORTHWEST CALIFORNIA AND SOUTHWESTERN OREGON...

Fairly robust disturbance over the Pacific will translate
southeastward towards the North-Central CA coast by the end of the
week with a persistent IVT pulse oriented southwest to northeast
into the coastal plain over the course of the forecast period
leading to waves of moderate precipitation to impact areas north of
the Bay area. Current progs indicate precip totals on the order of
2-4" with locally higher embedded within the coastal ranges
spanning north of Santa Rosa. Current rates anticipated to be
modest with upwards of 0.5-0.75"/hr at peak intensity lending to a
lower end threat for flash flooding, however totals are significant
enough to warrant a low-end threshold MRGL, mainly for the coastal
urban areas of Northwest CA up through Southwestern OR where
totals will be on the order of 2-4", especially into the windward areas
of the Klamath Range. MRGL was generally maintained from previous
forecast with only some minor modifications to align with the
latest guidance.

Kleebauer
$$
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FOUS30 KWBC 120805
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
305 AM EST Thu Dec 12 2024

Day 1
Valid 12Z Thu Dec 12 2024 - 12Z Fri Dec 13 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Kleebauer


Day 2
Valid 12Z Fri Dec 13 2024 - 12Z Sat Dec 14 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF NORTHWEST CALIFORNIA AND SOUTHWESTERN OREGON...

The overall forecast maintained a general continuity in the
expected synoptic evolution of a weak atmospheric river transpiring
across the Northwest CA coast, extending northward into Southwest
OR. IVT signatures between 700-1000 kg/ms will advect into the
coastal plain with some protrusion inland on the initial surge as
the southwest to northeast alignment of the pulse relegates a
majority of the moisture into the coast and adjacent coastal ranges
that will garner the greatest QPF just given the upslope component
of the wind field. A widespread 2-4" with local max of 5-5.5" is
forecast over the period with the general maxima likely within the
coastal King Range as is customary with IVT pulses exhibiting a
southwestern angle of approach across Northern CA. Rainfall rates
on the order of 0.25-0.5"/hr will be most common within these bands
of precipitation, however a few instances of >0.5"/hr might be
realized during the period between 00-12z Saturday when the primary
surge is forecast amongst the 00z deterministic suite. This
correlates well with the anticipated IVT maximum making headway
into the coastal plain which could lead to localized flooding
concerns in the expected zone(s) of impact. As of this juncture,
the heaviest rainfall will lie north of Santa Rosa with the primary
areas of interest likely positioned from the King Range up US101 to
the southern half of the Siskiyou in southwestern OR. With this
alignment, very little change was necessary from the previous MRGL
risk issuance, thus the forecast was relatively unchanged as the
MRGL risk was sufficient in consensus.

Kleebauer


Day 3
Valid 12Z Sat Dec 14 2024 - 12Z Sun Dec 15 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF NORTHWEST CALIFORNIA INTO THE CENTRAL SIERRA FOOTHILLS...

Atmospheric River setup from the previous period will translate
into D3 with a greater inland protrusion of the IVT pulse as the
upper level trough and associated surface low pivot onshore with
an expected wind shift that will mute heavier rain prospects along
the coast and eventually inland as we move into the second half of
the period. The threat is currently very marginal in nature within
the confines of the inland topography with the eastern foothills
of the Sierra's being the furthest east expanse of any heavy rain
threat, but even that is bordering on the lower end of a risk
threshold. This period is more of the transition point in the
pattern as the event will see a general decay in total rainfall and
overall rates as the system moves inland. There is a further south
push of the IVT pulse in the early portions of Saturday with some
modest dynamical element involved as the 500mb vorticity evolution
does bring some significant forcing towards the North- Central CA
coastal plain with impacts to places like Santa Rosa down into the
Bay area. Thankfully the pattern is progressive, but a quick 1-2"
is within the realm of possibility for a mainly urban zone which
could bring about some localized flooding prospects before the
disturbance moves inland and we get a quick end to the chances.

A MRGL risk continues for a good portion of Northwest CA with the
risk area now extending down into the Bay area compared to the
previous D2 alignment. A MRGL risk is also located at the base of
the Sierra foothills for locations below 5500ft.

Kleebauer
$$
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FOUS30 KWBC 130826
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
326 AM EST Fri Dec 13 2024

Day 1
Valid 12Z Fri Dec 13 2024 - 12Z Sat Dec 14 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
NORTHWEST CALIFORNIA...

Maintained the Slight Risk area over portions of northwest
California with only minor adjustments needed based on latest
deterministic and ensemble guidance. Rainfall should be growing in
both areal coverage and intensity today as a plume of moisture is
directed from the eastern North Pacific into northwest California.
Event total rainfall amounts through early Saturday morning are
still forecast to be in the 3 to 5 inch range across the Slight
Risk area. By late tonight/early Saturday morning the heavier rain
will shift southward as a strong mid level shortwave approaches the
region. This feature will act to increase large scale ascent,
while also cooling the mid levels enough to allow for some weak
instability to develop within the IVT axis. The 13/00Z HREF
neighborhood probabilities of rainfall exceeding 0.5" in an hour
are over 50% across most of the Slight risk...both across the most
favored upslope areas and also within a narrow southward shifting
axis of stronger convergence. This does not appear to be a high end
event given the progressive nature of the system...although some
creek and stream flooding and a few mudslides will be possible.

Bann


Day 2
Valid 12Z Sat Dec 14 2024 - 12Z Sun Dec 15 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
NORTHWEST CALIFORNIA...

Rainfall associated with an atmospheric river will be on-going as
the Day 2 period begins at 14/12Z...with the plume of deepest
moisture continuing to be directed in to parts of northwest
California although the axis of heaviest rainfall rates/amount will
be gradually be easing eastward in time with the main shortwave
while being shunted southward ahead of the surface cold front.
southward with time. The higher rates should quickly diminish with
the departure of the shortwave moves...with the risk of heavy rain
over by 18z. Thus this Slight risk is really only for the first few
hours of this day 2 period.

Bann

Day 3
Valid 12Z Sun Dec 15 2024 - 12Z Mon Dec 16 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.|

Bann
$$
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FOUS30 KWBC 140829
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
329 AM EST Sat Dec 14 2024

Day 1
Valid 12Z Sat Dec 14 2024 - 12Z Sun Dec 15 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
COASTAL CALIFORNIA FROM SANTA ROSA INTO SAN Francisco AND SAN JOSE...

Even though a much of the areal coverage of moderate to locally
heavy rainfall associated with an atmospheric river has already
moved on shore...maintained the Slight risk area mainly along the
coast from Santa Rosa southward into San Francisco and San Jose
given an expected up-tick in rainfall rates as a compact shortwave
trough approaches from the west. Short term guidance from the
convective allowing mesoscale guidance shows several hundred Joules
per kilogram of CAPE moving into that portion of California
immediately ahead of the shortwave impulse. The 14/00Z HREF
maintained a nearly 100 pct chance of half-inch per hour rainfall
rates and nearly 40 percent chance of 1 inch per hour rates over
and near the San Francisco Bay area during the early- to mid-
morning hours. The combination of the rainfall rates and the
urbanization of the area still points to an elevated risk of flood
impacts. The overall impacts should be limited by the fairly short
duration of heaviest rainfall...which looks to taper off quickly in
the 15Z to 18Z period.

Bann


Day 2
Valid 12Z Sun Dec 15 2024 - 12Z Mon Dec 16 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Bann


Day 3
Valid 12Z Mon Dec 16 2024 - 12Z Tue Dec 17 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent

Bann
$$
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FOUS30 KWBC 170751
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
251 AM EST Tue Dec 17 2024

Day 1
Valid 12Z Tue Dec 17 2024 - 12Z Wed Dec 18 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ALONG PORTIONS OF
THE EAST CENTRAL TO SOUTHEAST COAST OF FLORIDA...

Model consensus is for increasingly active showers late Tuesday
afternoon into Tuesday night/early Wednesday along the east central
to southeast coast of Florida. Low level easterly to southeasterly
flow in an axis of PW values 1.5 to 2+ standard deviations above
the mean expected to persist into the east central to southeast
Florida coast, with models showing an axis of defined boundary
layer convergence in this low level inflow axis parallel to the
east central to southeast coast. There will be potential for very
slow moving cells along the coastal regions, supporting locally
very heavy rainfall amounts and an urban flash flood threat. HREF
neighborhood probabilities are high (50-90%) for 3"+ amounts from
Cape Canaveral, south to Miami, while the 5"+ neighborhood
probabilities are high (60-90%) from near West Palm Beach, south to
Miami. The best hi res overlap, evident in the greatest EAS
probabilities for 2"+ amounts, is from near West Palm, south to
just north of Miami.

Oravec


Day 2
Valid 12Z Wed Dec 18 2024 - 12Z Thu Dec 19 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Oravec


Day 3
Valid 12Z Thu Dec 19 2024 - 12Z Fri Dec 20 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Oravec
$$
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FOUS30 KWBC 180823
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
323 AM EST Wed Dec 18 2024

Day 1
Valid 12Z Wed Dec 18 2024 - 12Z Thu Dec 19 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ALONG PARTS OF THE
OHIO AND TENNESSEE VALLEYS ALONG WITH THE SOUTHEAST FLORIDA COAST...

...Parts of the Mid-South to Lower Ohio Valley...
Maintained the Marginal Risk area across parts of western and central
Tennessee into southern Kentucky as models still advertise an
upper-level trough amplifying to the west which allows for a more
curved upper level jet streak on the lee side of the trough. That
configuration may result in some enhanced rainfall rates...an idea
supported by the 18/00Z HREF neighborhood probabilities showing
potential for rainfall rates exceeding an inch per hour between
12-18Z today (mainly in Tennessee). With rainfall blossoming to
the west of the outlook area in the pre-dawn hours this morning
helping to prime the soils a bit more and a general slowing of the
eastward progression across the Tennessee Valley compared with
earlier forecasts...opted to extend the Marginal risk area a bit
farther westward than previously indicated. The HREF probability of
exceeding flash flood guidance remained low but did reflect
somewhat higher probabilities west of the same guidance from the
17/12Z and 17/18Z runs. The decision to expand westward slightly
was also driven by the observed rainfall during the past day or two
over parts of northwest Tennessee and southwest Kentucky which has
resulted in the latest 1-hour and 3- hour flash flood guidance
coming down and the 0-40km soil moisture percentiles per NASA SPoRT
have climbed to 60-80% for most areas.

...Southeast FL...
Post frontal easterly low level flow off the Atlantic will linger
allowing for a possible repeat of convective clusters over and
near the southeast Florida coastline today. The 00Z runs of the
high-res CAMs continued to show onshore low-level moisture
flux/convergence and sufficient deep-layer instability to support
localized downpours. The 18/00Z HREF supports rates of 2+ inch per
hour peaking around 10 percent during the afternoon with and a
50-70 percent 40km neighborhood probabilities of at least 5 inches
of additional rain and 30-50 percent probabilities of 8+ inches.
Given that these numbers are comparable with the 17/12Z and 17/18Z
runs of the HREF...saw little reason to make too many changes other
than nudges to the boundary of the previously issued Marginal risk
area.


Bann

Day 2
Valid 12Z Thu Dec 19 2024 - 12Z Fri Dec 20 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Bann


Day 3
Valid 12Z Fri Dec 20 2024 - 12Z Sat Dec 21 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Bann
$$
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FOUS30 KWBC 210756
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
256 AM EST Sat Dec 21 2024

Day 1
Valid 12Z Sat Dec 21 2024 - 12Z Sun Dec 22 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Kleebauer


Day 2
Valid 12Z Sun Dec 22 2024 - 12Z Mon Dec 23 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Kleebauer


Day 3
Valid 12Z Mon Dec 23 2024 - 12Z Tue Dec 24 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
NORTHERN CALIFORNIA AND SOUTHWEST OREGON...

The next, more prominent atmospheric river is forecast to impact
the NorCal coast into southwestern OR by the end of the D2 into D3
time frame with a better aligned IVT pulse anticipated for areas
that saw significant rainfall totals over the past 7-10 days. The
heaviest rain will be confined to the immediate coast with a
southwest to northeast oriented moisture flux expected leading to
upslope flow a bit orthogonal to the coastal terrain extending from
the King Range up through the Siskiyou in southwest OR. Current
forecasted totals within the ensemble suite are between 2-4" with
some deterministic output between 4-5" at max. This is generally
within the confines of a low-end MRGL risk threshold when assessing
historical precedence for these types of events. The main
difference between this event and the previous was the primary
hydrometeor will come in the form of rainfall, even inland as lower
heights will be confined offshore and a flood of warmer air in the
boundary layer will protrude inland. Only the highest elevations of
the Northern Sierra and Mount Shasta will have a higher threat for
winter ptypes, so this points some of the more sensitive areas of
northern CA into play where burn scar remnants are located.

The inherited MRGL from the D4 was relatively maintained for the
areas outlined in CA, but the prospects for flash flooding were
pretty low given the QPF signature for locations north of
southwestern OR, so decided to pull back the northern extension
along the OR coast. The MRGL extends inland to include those more
sensitive areas within the complex terrain, even extending to the
foothills of the Northern Sierra where heavier precip will make its
way by the end of the forecast cycle and likely carrying beyond to
the D4 period.

Kleebauer
$$
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FOUS30 KWBC 220759
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
259 AM EST Sun Dec 22 2024

Day 1
Valid 12Z Sun Dec 22 2024 - 12Z Mon Dec 23 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

There is a non-zero opportunity for isolated flash flood concerns
across portions of the eastern FL coastline, mainly along the Space
Coast near Coco Beach up to Cape Canaveral and Titusville. A
developing surface trough off the coast will nose into the
coastline later this evening with flow turning more perpendicular
to the coast allowing for increased frictional convergence in a
small zone within the trough. HREF neighborhood probabilities are
hovering around 20-30% at peak for >3" in any spot within the area
above, very much on the lower end of any flash flood threshold, and
mainly below the current FFG indices for 1/3/6 hr time frames.
More robust deterministic has closer to 4.5-5" over a short period
of time the back end of the forecast period, but most of the CAMs
maintain the heaviest precip offshore. The prospects are very low,
but wanted to make mention that threat is non-zero.

Kleebauer


Day 2
Valid 12Z Mon Dec 23 2024 - 12Z Tue Dec 24 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
NORTHERN CALIFORNIA AND SOUTHWEST OREGON...

Consensus continues to grow for a quick hitting weak to borderline
moderate atmospheric river aimed at southwestern OR down into
northern CA by late Monday into Tuesday morning. Recent ensemble
depictions are in agreement on an IVT pulse centered over the
northern CA coast, protruding inland through the end of the period
with warm air advecting well into the boundary layer and above
yielding a majority rainfall signal across even some of the higher
terrain inland. NAEFS output for PWAT anomalies indicates a tongue
of 2-3 deviations above normal moisture plume being ushered in on
deep layer southwest flow thanks to a shortwave trough undercutting
a broad upper level cyclone located off the PAC Northwest coast.
This look is fairly textbook for a period of prevailing
southwesterly flow running orthogonal to some of the adjacent
coastal ranges that are situated from southwest OR down through
northern CA. The zones most impacted will lie at the foothills of
Mount Shasta and the northern Sierra Nevada for the inland portion,
as well as the King and Siskiyou Ranges that align from OR down
through northwestern CA. Rainfall totals on the order of 3-5" with
locally higher in the highest elevations of the above ranges are
forecast during the time frame beginning 21z Monday through 12z
Tuesday with some carryover into D3 before the main shortwave moves
inland. 2-4" will be common within the coastal plain with locally
higher in areas south of Eureka. Localized flooding prospects are
higher than normal given the stronger IVT pulse being depicted,
also impacting areas that saw decent rainfall as of a week to 10
days prior. The saving grace is the time frame is not very long in
terms of impact, so that helps limit a greater flash flood threat.

The previously inherited forecast was generally maintained outside
some fine tuning across the Sierra Foothills and the northern
periphery of the MRGL risk into OR.

Kleebauer


Day 3
Valid 12Z Tue Dec 24 2024 - 12Z Wed Dec 25 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR THE NORTHERN
SIERRA FOOTHILLS AND EAST TEXAS INTO THE LOWER MISSISSIPPI VALLEY...

..Sierra Foothills..

Atmospheric river from previous period will bleed into the D3 time
frame with the primary shortwave trough quickly propagating inland
with increased forcing upon arrival into the Northern and Central
Sierra, less so for areas back into the coast due to negative
vorticity advection. Locally enhanced rainfall will be plausible
the initial portion of the period with the heaviest likely aligned
along those Foothill regions of the Northern Sierra, mainly within
elevations below 8000ft, although snow levels will fall below
7000ft towards the end of the more significant precipitation time
frame Tuesday morning. Additional totals of 1-3" are possible
within a 6-10 hour window prior to the precip ending leading to a
low-end potential for flash flood concerns just outside the
Valley that extends from Redding down to Sacramento. Higher runoff
capabilities due to terrain orientation and soil moisture anomalies
running closer to normal will present some potential for flood
concerns despite this being an event that doesn't maintain a more
prolonged precipitation signature. Considering limited deviation
from run-to-run amongst guidance with considerable agreement in
timing and magnitude of precipitation, continuity from the previous
forecast was maintained with very little in the way of adjustment
in the inherited MRGL risk across the Sierra Foothills.

..Arklatex and Lower Mississippi Valley..

Surface ridge to the northeast will slowly drift further to the
northeast allowing for a more broad return flow regime to affect
areas across the Western Gulf into the Lower Mississippi Valley.
Southerly flow will advect a bit more unstable air northward with
areal theta_E averages on the increase when assessing the ensemble
means and initial D3 cluster analysis with heavy weight towards the
GEFS and ECENS output. Aloft, a shortwave will dig southeast with
enhanced mid-level energy accompanying aiding in better regional
forcing as we work into Tuesday afternoon and evening. This will
help setup a period of convective initiation across Eastern TX and
points north with the primary axis of heaviest precip likely
aligned southwest to northeast across the Arklatex down into the
eastern Hill Country located east of I-35. Weak jet coupling will
help with the expansion of the precip field across the above areas
with those embedded convective signatures likely situated along and
ahead of an advancing cold front as surface cyclogenesis in-of the
Red River will become a focus for activity in question. Locally
heavy rainfall will be forecast within those stronger convective
cores, however the PWAT anomalies and available surface based
instability will be modest, at best with regards to the setup. This
will likely lead to more spotty instances of >3" of total precip
in any one location with the best areas of interest mentioned above.

The previous MRGL risk was maintained, but did trim some of the
eastern flank of the risk area as probabilities off the blend are
pretty meager and agree with the current ML output basing best
chances to the northwest of where the risk area was drawn. A small
extension to the southwest was done out of prospects for the
traditional southwestern bias in heavier QPF within these types of
setups. This was featured within a few of the regional
deterministic and works well with the proposed elevated SBCAPE
anticipated in that area.

Kleebauer
$$
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