FOUS30 KWBC 200757
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
257 AM EST Thu Feb 20 2025

Day 1
Valid 12Z Thu Feb 20 2025 - 12Z Fri Feb 21 2025

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

Wegman


Day 2
Valid 12Z Fri Feb 21 2025 - 12Z Sat Feb 22 2025

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

Wegman


Day 3
Valid 12Z Sat Feb 22 2025 - 12Z Sun Feb 23 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR MUCH OF
WESTERN WASHINGTON STATE AND COASTAL OREGON...

A pair of frontal disturbances are expected to move into the coast
of the Pacific Northwest on Saturday. These disturbances will have
peak integrated vapor transport (IVT) values around 700 kg/ms as
they move ashore within a 130+ kt upper level jet. With that level
of moisture advection off the Pacific, areas of heavy rain are
expected, especially into the coastal ranges of Oregon and
Washington as well as into the Cascades. Rain rates may reach up
to a half inch per hour at times. Snow levels with these systems
will be high enough (between 7,000 and 8,500 ft MSL) that much of
the precipitation falling west of the Cascades will be in the form
of rain. Colder air will remain in place further inland,
especially into the higher elevations of Idaho and Montana so the
flooding threat there will be near zero. West facing slopes will
receive the greatest rainfall amounts Saturday and especially
Saturday night, and it's along these slopes and their adjacent
valleys where any isolated flash flooding may occur. Since most of
the Marginal risk area is already very flood resistant, this is a
lower-end Marginal Risk.

Wegman

$$
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FOUS30 KWBC 210819
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
319 AM EST Fri Feb 21 2025

Day 1
Valid 12Z Fri Feb 21 2025 - 12Z Sat Feb 22 2025

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

Oravec


Day 2
Valid 12Z Sat Feb 22 2025 - 12Z Sun Feb 23 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR MUCH OF
WESTERN WASHINGTON STATE AND COASTAL OREGON...

No significant changes made to the previous marginal risk across
coastal sections of Oregon, Washington and in the upslope of the
Washington Cascades and northern Oregon Cascades. The beginning of
a two day atmospheric river event on tap as broad west
southwesterly mid to upper level flow is established across the
northeast Pacific toward the Pacific Northwest. PW anomalies
expected to rise to 2 to 3+ standard deviations above the mean by
Saturday afternoon with the lead shortwave moving toward the Pac NW
coast and continue at that level into Sunday morning. Strong
850-700 mb moisture flux, anomalies 2 to 4+ standard deviations
above the mean expected in the anomalous PW axis, max IVT values
600-800 kg/m/s. This will support hourly rainfall rates of .50"+
and widespread totals of 1-2"+ and max totals of 3-5"+ in favored
terrain regions. Snow levels will be very high day 2 across the
Pac NW, with much of the precipitation falling as rain. This heavy
rain, combined with snow melt will support isolated runoff issues. Precipitation has been below average over the past month over the
Pac NW, which should mitigate any widespread runoff issues day 1.

Oravec


Day 3
Valid 12Z Sun Feb 23 2025 - 12Z Mon Feb 24 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR MUCH OF
WESTERN WASHINGTON STATE AND COASTAL OREGON AND NORTHERN IDAHO INTO
NORTHWEST MONTANA...

The atmospheric river event that started day 2 into the Pacific
Northwest will continue into day 3 as additional height falls
embedded in the broad west southwest mid to upper level flow across
the northeast Pacific move toward the Pacific Northwest.
No significant changes to the plume of anomalous PW values and
anomalous 850-700 mb moisture flux anomalies impacting the Pac NW
day 3, with values 2-4+ standard deviations above the mean
persisting along with max IVT values of 600-800 kg/m/s. This will
support another day of widespread heavy rainfall totals of 1-2"+
and max totals in the 3-5"+ range in the favored terrain regions.
Snow levels again will remain high across much of the Pac NW day 3
with much of the precip again falling as rain. With widespread two
day totals in the 3-5"+ range and max totals 6-10" in favored
terrain regions, increasing soil moisture and stream flow values
will increase the risk of flooding.

A marginal risk area was added inland across portions of northern
Idaho into northwest Montana. The anomalous PW values pushing into
the Pac NW day 2 will move into the Northern Rockies day 3, with
values 2-3+ standard deviations above the mean. Similar to areas
across the Pac NW, snow levels will be very high day 3 with much of
the precip falling as rain . Two day precip totals of 1-3"
possible across northern Idaho into northwest Montana, combined
with snow melt will support isolated runoff conditions developing.

Oravec

$$
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FOUS30 KWBC 220903
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
403 AM EST Sat Feb 22 2025

Day 1
Valid 12Z Sat Feb 22 2025 - 12Z Sun Feb 23 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR MUCH OF
WESTERN WASHINGTON STATE AND COASTAL OREGON...

No significant changes made to the previous marginal risk across
coastal sections of Oregon, Washington and in the upslope of the
Washington Cascades and northern Oregon Cascades. The beginning of
a multi day atmospheric river/heavy rainfall event on tap as broad
west southwesterly mid to upper level flow is established across
the northeast Pacific toward the Pacific Northwest. PW anomalies
expected to rise to 2 to 3+ standard deviations above the mean by
Saturday afternoon with the lead shortwave moving toward the Pac NW
coast and continue at that level into Sunday morning. Strong
850-700 mb moisture flux, anomalies 2 to 4+ standard deviations
above the mean expected in the anomalous PW axis, WITH max IVT
values 600-800 kg/m/s. This will support max hourly rainfall rates
of .50"+ and widespread totals of 1.5-2.5"+ and max totals of 3-5"+
in favored terrain regions. The marginal risk area fits well with
where the HREF neighborhood are high for 3"+ totals day 1.

The greatest HREF neighborhood probabilities for .50"+/hr rates
are through the Olympic Range into the southern WA Coast Range from
2100 UTC Sat to 0200 UTC Sun, with probabilities in the 60-90%
range and across portions of the WA Cascades from 2300 UTC Sat to
0400 UTC Sun where probabilities peak in the 60-80% range. Snow
levels will be very high day 1 across the Pac NW, with much of the precipitation falling as rain. This heavy rain, combined with snow
melt will support isolated runoff issues. The higher hourly rates
do not last for more than a few hours day 1 across the NW. This
combined with been below average precipitation amounts over the
past month over the Pac NW, should mitigate any widespread runoff
issues day 1.


Day 2
Valid 12Z Sun Feb 23 2025 - 12Z Mon Feb 24 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM THE NORTHERN
OREGON COAST RANGE INTO THE OLYMPIC RANGE AND OVER THE SOUTHERN
WASHINGTON CASCADES...

The atmospheric river event that started day 1 into the Pacific
Northwest will continue into day 2 as additional height falls
embedded in the broad west southwest mid to upper level flow across
the northeast Pacific move toward the Pacific Northwest. The second
surge of high IVT values, 600-800 kg/m/s and anomalous PW and
850-700 mb moisture flux values, 2-4+ standard deviations above the
mean will push back into the coastal Pac NW Sunday morning. This
will support another day of widespread heavy rainfall totals of
1-2"+ and max totals in the 3-5"+ range in the favored terrain
regions. Snow levels again will remain high across much of the Pac
NW day 2 with much of the precip again falling as rain. With
widespread two day totals in the 3-5"+ range and max totals 6-10"
in favored terrain regions, increasing soil moisture and stream
flow values will increase the risk of flooding. Given this, slight
risk areas were added from the northern OR coast range, northward
into the Olympic Range and over the southern WA Cascades.

No significant changes to the marginal risk area inland across far
northeast OR, far eastern WA state into northern ID and northwest
MT. The anomalous PW values pushing into the Pac NW day 1 will
move into the Northern Rockies day 2, with values 2-3+ standard
deviations above the mean. Similar to areas across the Pac NW, snow
levels will be very high day 2 with much of the precip falling as
rain. Two day precip totals of 1-3" possible across northern Idaho
into northwest Montana, combined with snow melt will support
isolated runoff conditions developing.

Oravec


Day 3
Valid 12Z Mon Feb 24 2025 - 12Z Tue Feb 25 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM THE NORTHERN
OREGON COAST RANGE INTO THE OLYMPIC RANGE AND OVER THE SOUTHERN
WASHINGTON CASCADES...

The next in the series of strong height falls in the broad west
southwesterly mid to upper level flow across the northeast Pacific
will push an amplifying trof into the Pac NW Monday. This third in
the series will be stronger than the previous two and support a
stronger surface low moving into the Olympic Peninsula/eastern
Vancouver Island area Monday evening. 850-700 mb moisture flux
values will again be anomalous..2-3+ standard deviations above the
mean, but PW values not expected to be as anomalous as the days 1
and 2 events, generally around 1 standard deviation above the mean.
This will result in slightly lower max IVT values, 500-600 kg/m/s
impacting the coastal Pac NW day 3. Additional widespread heavy
rains of 1-2" likely from the Olympics, south along the Oregon
Coast Range and into the WA Cascades and northern OR Cascades. This
will bring 3 day totals into the 7-10 inch range from the northern
OR Coast Range into the Olympic Range and through much of the WA
Cascades. Increasing soil moistures and stream flows will continue
a flooding threat into day 3. Slight risks introduced day 2 were
maintained day 3 across the southern WA Cascades and from the
northern OR Coast Range and Olympic Range.

...Southeast Florida...
While there are some timing differences among the latest suite of
guidance, there is agreement on an amplifying upper trof across
the western to central Gulf Monday and into the eastern Gulf by
early Tuesday. Strengthening southerly to southwesterly low level
flow off the Gulf will push anomalous PW and 850-700 mb moisture
flux values, 2 to 3+ standard deviations above the mean, across
South Florida early day 3. This will support the potential for an
area of heavy rains to push across South Florida Monday into Monday
evening, with timing differences evident between the 00Z EC, GFS
and NAM which have detail differences with the amplitude of the
upper trof. While confidence is not great with the details of the
upper trof amplitude and resultant timing of the strongest UVVS,
there is consensus for heavy rains to push across South Florida day
3. A marginal risk area was added for the urban areas of southeast
coastal Florida from Miami to West Palm for the potential for
isolated urban runoff issues.

Oravec

$$
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FOUS30 KWBC 230757
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
257 AM EST Sun Feb 23 2025

Day 1
Valid 12Z Sun Feb 23 2025 - 12Z Mon Feb 24 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS THE OREGON
COAST INTO THE OLYMPIC RANGE AND OVER PORTIONS OF THE SOUTHERN
WASHINGTON AND NORTHERN OREGON CASCADES...


The ongoing atmospheric river event across the Pac NW will continue
during the upcoming day 1 period as additional height falls
embedded in the broad west southwest mid to upper level flow across
the northeast Pacific move toward the Pacific Northwest. The next
surge of high IVT values, 600-800 kg/m/s and anomalous PW and
850-700 mb moisture flux values, 2-4+ standard deviations above the
mean will push back into the coastal Pac NW during the first half
of day 1. This will support another day of widespread heavy
rainfall totals of 1.5-2.5"+ and max totals in the 3-5"+ range in
the favored terrain regions. Snow levels again will remain high
across much of the Pac NW day 1 with much of the precip again
falling as rain. This will bring widespread two day totals in the
3-5"+ range and max totals 6-10" in favored terrain regions,
increasing soil moisture and stream flow values and increasing the
risk of flooding. No significant changes were made to the slight
risk along the OR coast range, northward into the Olympic Range and
over the southern WA Cascades into much of the OR Cascades.

No significant changes to the marginal risk area inland across far
northeast OR, far eastern WA state into northern ID and northwest
MT. The anomalous PW values that pushed into the Pac NW over the
past 24 hours will move into the Northern Rockies day 1, with
values 2-3+ standard deviations above the mean. Similar to areas
across the Pac NW, snow levels will be very high day 1 with much
of the precip falling as rain. Precip totals of 1-2" possible day
1 across northern Idaho into northwest Montana, combined with snow
melt will support isolated runoff conditions developing.

Oravec


Day 2
Valid 12Z Mon Feb 24 2025 - 12Z Tue Feb 25 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM THE NORTHERN
OREGON COAST RANGE INTO THE OLYMPIC RANGE AND OVER THE SOUTHERN
WASHINGTON CASCADES...

The next in the series of strong height falls in the broad west
southwesterly mid to upper level flow across the northeast Pacific
will push an amplifying trof into the Pac NW Monday. This third in
the series will be stronger than the previous two and support a
stronger surface low moving into the Olympic Peninsula/eastern
Vancouver Island area Monday evening. 850-700 mb moisture flux
values will again be anomalous..2-3+ standard deviations above the
mean, but PW values not expected to be as anomalous as the two
previous events, generally around 1 standard deviation above the
mean. This will result in slightly lower max IVT values, 500-600
kg/m/s impacting the coastal Pac NW day 2. Additional widespread
heavy rains of 1-2" likely from the Olympics, south along the
Oregon Coast Range and into the WA Cascades and northern OR
Cascades. This will bring totals beginning Sat through the day 2
period in the 7-10 inch range from the northern OR Coast Range into
the Olympic Range and through much of the WA Cascades. Increasing
soil moistures and stream flows will continue a flooding threat
into day 2. Slight risks were maintained day 2 across the southern
WA Cascades and from the northern OR Coast Range and Olympic Range.

...Southeast Florida...
Similar to the past few model cycles, there are some timing
differences among the latest suite of guidance with the amplifying
upper trof moving across the western to central Gulf Monday and
into the eastern Gulf by early Tuesday. Strengthening southerly to southwesterly low level flow off the Gulf will push anomalous PW
and 850-700 mb moisture flux values, 2 to 3+ standard deviations
above the mean, across South Florida early day 2. Well defined
upper diffluence ahead of the amplifying upper trof will support
the potential for one or more areas of heavy rains to push across
South Florida Monday into Monday evening/early Tuesday. There seems
to be some consensus in the hi res runs for an initial area of
heavy rains to impact South Florida Monday afternoon, followed by a
second round sometime between 0000 and 1200 UTC Tue. With each
round of heavy rain, there may be localized hourly amounts of 1-2",
supporting isolated runoff issues in the urban portions of
Southeast Florida. No changes made to the previous marginal risk
area from Miami to West Palm Beach.

Oravec


Day 3
Valid 12Z Tue Feb 25 2025 - 12Z Wed Feb 26 2025

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

Oravec

$$
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FOUS30 KWBC 240801
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
301 AM EST Mon Feb 24 2025

Day 1
Valid 12Z Mon Feb 24 2025 - 12Z Tue Feb 25 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM THE NORTHERN
OREGON COAST RANGE INTO THE OLYMPIC RANGE AND OVER THE SOUTHERN
WASHINGTON CASCADES...

...Pacific Northwest...

A vigorous shortwave trough supporting a 985 mb surface low will
race into the coast of the Pacific Northwest tonight. Its leading
cold front will move into the Oregon and Washington coasts today
and spread inland through tonight. Upslope flow into the Olympics,
coastal ranges, and Cascades will all locally enhance the rainfall rates...which at times may exceed an inch per hour. NASA Sport
soil moisture imagery shows the soils across nearly all of
Washington, Oregon, and Idaho are at or near saturation in the
surface layer. This should allow the rainfall from the front moving
into the region today to mostly convert to runoff. Integrated
Vapor Transport values will peak around 500 kg/ms across coastal
Washington. These values are far from impressive, so those very
favorable antecedent soil moisture will play a major role in the
potential for flooding. Part of the reason for the lower IVT values
is the predominant south to southwesterly flow, which is at an
oblique The typical urban areas, low- lying and flood- prone areas,
and narrow valleys will be at greatest risk for flash flooding,
especially south and west facing slopes.

Snow levels will rise to as high as 7,000 ft. ahead of and through
frontal passage for southwest Washington and all of western Oregon
through the day. As colder air moves in post-frontal passage, the
snow levels will crash to around 3,500 ft area-wide. The lower snow
levels will allow much of the heaviest precipitation falling into
the mountains to remain as snow, and thus reduce the flooding risk
through the overnight. Dynamic cooling on the windward side of the
mountains may further reduce the amount of precipitation that
converts to runoff due to locally reduced snow levels.

No significant changes were made to the inherited Slight and
Marginal risk areas across the Pacific Northwest. The low is
already well-formed and will continue intensifying as it approaches
the Pacific Northwest tonight. A few very minor tweaks were made to
exclude some of the higher elevations from the flood risk areas due
to falling snow levels tonight.

...Southeast Florida...

A positively tilted trough traversing the Gulf this morning will
intensify as it becomes more neutrally tilted, thus increasing the
divergence ahead of the trough. A few persistent thunderstorms are
making their way in the general direction of the Florida Keys this
morning. The latest HRRR guidance suggests the heaviest
thunderstorms will pass south of the Marginal Risk area that covers
from West Palm Beach to Miami. Nonetheless heavy rain and potential
for training are still possible, prompting the continuance of the
Marginal Risk in this area with no changes. This remains a very
low-end Marginal Risk threat with much of South Florida in a dry
period, and should any flooding occur, it will likely be in poor-
drainage and urban areas.

Wegman


Day 2
Valid 12Z Tue Feb 25 2025 - 12Z Wed Feb 26 2025

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

Wegman

Day 3
Valid 12Z Wed Feb 26 2025 - 12Z Thu Feb 27 2025

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

Wegman

$$
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FOUS30 KWBC 250750
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
250 AM EST Tue Feb 25 2025

Day 1
Valid 12Z Tue Feb 25 2025 - 12Z Wed Feb 26 2025

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

Lingering but diminishing rainfall will continue into the coastal
ranges of southwest Washington and northwest Oregon through the
morning. See MPD #52 at wpc.ncep.noaa.gov/metwatch/metwatch_mpd_multi.php?md=0052&yr=2025
for more details on the local heavy rain threat.

Wegman


Day 2
Valid 12Z Wed Feb 26 2025 - 12Z Thu Feb 27 2025

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

Wegman

Day 3
Valid 12Z Thu Feb 27 2025 - 12Z Fri Feb 28 2025

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

Wegman

$$
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FOUS30 KWBC 011535
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1035 AM EST Sat Mar 1 2025

Day 1
Valid 12Z Sat Mar 01 2025 - 12Z Sun Mar 02 2025

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

Cook/Roth


Day 2
Valid 12Z Sun Mar 02 2025 - 12Z Mon Mar 03 2025

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

Roth


Day 3
Valid 12Z Mon Mar 03 2025 - 12Z Tue Mar 04 2025

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

...Southeast Oklahoma...
A cold low progresses from the Great Basin into the High Plains of
CO by Tuesday morning. This leads to the formation of a CO cyclone
late Monday which advances eastward across southwest KS. Warm air
advection ahead of the cyclone is expected to advect 500-1000 J/kg
of MU CAPE and precipitable water values of 1.25"+ by Tuesday
morning into southeast OK. Inflow at 850 hPa accelerates past 50
kts. Since the airmass in the wake of its cold front is more dry
than cold, instability lurks in its "cold sector" as well. NAM
parameters suggest organized convection should occur either in the
form/mode of supercells or a squall line -- assuming convection is
around for 4+ hours and can form a cold pool to force forward
propagation -- somewhere near southeast OK. For the moment, only
the 00z Canadian Regional model brings rainfall amounts over 1.5"
(local spots of 3-4" near the Red River Valley of the South). The
region has been dry over the past week, allowing much of the
ArkLaTex and southeast OK (outside of the Ouachita mountains) to
not be particularly sensitive to heavy rainfall should the 00z
Canadian verify. While the risk of excessive rainfall is non- zero,
believe it still remains under the 5 percent threshold for the
time being.

Roth

$$
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FOUS30 KWBC 020842
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
342 AM EST Sun Mar 2 2025

Day 1
Valid 12Z Sun Mar 02 2025 - 12Z Mon Mar 03 2025

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

Churchill


Day 2
Valid 12Z Mon Mar 03 2025 - 12Z Tue Mar 04 2025

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

Churchill


Day 3
Valid 12Z Tue Mar 04 2025 - 12Z Wed Mar 05 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE UPPER MIDWEST AND MIDDLE MISSISSIPPI VALLEY INTO PORTIONS OF
THE LOWER MISSISSIPPI VALLEY AND TENNESSEE VALLEY...

A pattern change will bring widespread precipitation to much of the
Central and Southeast CONUS, as a cut-off low/upper-level trough
and associated surface cyclone progress across the middle portion
of the country. QPF maxima are expected across two general regions,
near the Mid-South (primarily in associated with precipitation from
the broad open warm sector and subsequent cold frontal passage)
and much of IA into northern MO (mainly from the pivoting low
pressure center as it occludes/matures). While flash flood impact
coverage should remain somewhat limited in both areas (low-end
Slight risk probabilities) with relatively dry antecedent
conditions and a rather progressive storm system motion, the very
dynamic nature of the system is likely to bring strong convection
with localized totals nearing 2" in a short period (though a
portion of the QPF over IA is likely to be in the form of snow on
the back-end of the low). Barring any major changes in the
forecast strength and progression of the storm system, impacts are
likely to be capped at the Slight threshold with better refinement
of the areas impacted with the addition of CAM data over the next
couple of days.

Churchill


$$
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FOUS30 KWBC 030710
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
210 AM EST Mon Mar 3 2025

Day 1
Valid 12Z Mon Mar 03 2025 - 12Z Tue Mar 04 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE SOUTHERN PLAINS...

Robust convective development is expected tonight across portions
of north central TX into central OK along a cold front. As
impressive forcing (strong mid-level shortwave and upper-level
divergence) overruns this front convection should quickly develop
by 06z. Activity will likely organize into a line pretty quickly
and then track eastward across north TX and OK. The expected quick
eastward motion of the cold front will likely limit the extent of
the flash flood risk. However with a 50-60kt south southwesterly
low-level jet developing and deep layer flow largely parallel to
the front, there should be some opportunity for brief convective
training. While the duration of training will not be very long, it
may locally be enough to exceed 2" in an hour of rainfall. Setups
like this tend to overachieve rainfall wise, and that will likely
be the case this time as well. Thus we still tend to think the new
00z HREF guidance is too dry (with the PMM suggesting localized
totals of ~1.5"), and there may still be an uptick in model QPF in
future runs (with totals in vicinity of one of the wetter models,
the 00z GEM-Reg, still quite possible). Overall, not anticipating
a significant flash flood threat, but localized, mainly urban,
flash flooding is a possibility.

Churchill/Chenard


Day 2
Valid 12Z Tue Mar 04 2025 - 12Z Wed Mar 05 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE UPPER MIDWEST AND PORTIONS OF THE MID-SOUTH INTO THE SOUTHEAST...

A pattern change will bring widespread precipitation to much of the
Central and Southeast CONUS, as a cut-off low/upper-level trough
and associated surface cyclone progress across the middle portion
of the country. QPF maxima continue to be expected across two
general regions, in and around the Mid-South (primarily in
associated with precipitation from the broad open warm sector and
subsequent cold frontal passage) and much of IA into northern MO
(mainly from the pivoting low pressure center as it occludes).
While flash flood impact coverage should remain somewhat limited in
both areas (low-end Slight risk probabilities) with relatively dry
antecedent conditions and a rather progressive storm system
motion, the very dynamic nature of the system is still likely to
bring periods of strong convection with localized totals nearing
2". While a portion of the QPF over IA is likely to be in the form
of snow on the back-end of the low, the expected 2" total will also
be relatively long duration, as rates will be limited to 0.5"/hr
with a relative lack of instability. Over the Mid-South and
Southeast, any localized 2" totals could occur over a much shorter
period of time (as little as an hour) as instability which be much
more plentiful. Barring any major changes in the forecast strength
and progression of the storm system, impacts are likely to be
capped at the Slight threshold with continued refinement to the
outlook with the addition of more CAM data over the next day or so.

Churchill


Day 3
Valid 12Z Wed Mar 05 2025 - 12Z Thu Mar 06 2025

...A MARGINAL RISK OF EXCESSIVE RAINFALL EXISTS FOR PORTIONS OF
SOUTHERN CALIFORNIA AND THE NORTHEAST...

...Southern California...
A cyclone moving towards the region at the base of an amplifying
and progressive West Coast upper level trough brings precipitable
water values near the coastal ranges above 1", with 0.75"+
extending into the deserts. While the strength of the low-level
inflow is modest -- 25+ kts -- the system has some instability to
work with which could allow for hourly rain totals to reach 0.5",
which would be most problematic in burn scars. Overall totals
appear to be capped near 3". The inherited Marginal Risk appears
reasonable, so changes to the area depicted were minimal.

...Northern Mid-Atlantic States/Southern New England...
A progressive deep layer cyclone moves through the Great Lakes into
Southeast Canada, bringing of shot of 60 kt inflow at 850 hPa into
the region with precipitable water values rising to 1-1.25".
Portions of PA, NY, and the southern coast of New England appear
to have some instability to work with, as MU CAPE of 250-500 J/kg
is forecast to be available. Along with low- to mid-level
frontogenesis, hourly rain totals to 1.25" should be possible.
While most of this area has had below average precipitation this
past week, a good portion of New England north of CT/RI/southeast
MA have 1-2" of snow water equivalent on the ground, so melting
snow should be occurring as well considering the strength of the
warm air advection which could raise both temperatures and dew
points well into the 40s. The inherited Marginal Risk both fits
the most recent QPF guidance and the ideas above, so changes to the
area depicted were minimal.

Roth

$$
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FOUS30 KWBC 031545
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1045 AM EST Mon Mar 3 2025

Day 1
Valid 12Z Mon Mar 03 2025 - 12Z Tue Mar 04 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE SOUTHERN PLAINS...

...16z update...

12z Hi-Res CAMs continue to depict run to run consistency with
small adjustments. Timing of initialization still appears to
be peaking in the 03-06z time window and from north (KS) to south
northern TX. CIRA LPW sfc-850mb moisture shows the dry slot from
yesterday's low level cyclone has started to erode with return
moisture coming through the Concho Valley with the dry line
orienting more WSW to ENE lifting north with Tds increasing from
10-20F into 50-low 60s. This orientation is a bit flatter to the
deeper steering flow once cells do develop/mature after 06z and may
allow for a tad higher potential for repeating/increased duration
of those intense rainfall rates. Still forward speeds will limit
overall totals and flash flooding is more likely to be limited to
urban/typical poor drainage areas that could be very quickly
inundated. Still overall expected totals are not likely to induce
large areas of flooding conditions and a Marginal Risk continues to
be appropriate risk level.

Gallina

---Prior Discussion---
Robust convective development is expected tonight across portions
of north central TX into central OK along a cold front. As
impressive forcing (strong mid-level shortwave and upper-level
divergence) overruns this front convection should quickly develop
by 06z. Activity will likely organize into a line pretty quickly
and then track eastward across north TX and OK. The expected quick
eastward motion of the cold front will likely limit the extent of
the flash flood risk. However with a 50-60kt south southwesterly
low-level jet developing and deep layer flow largely parallel to
the front, there should be some opportunity for brief convective
training. While the duration of training will not be very long, it
may locally be enough to exceed 2" in an hour of rainfall. Setups
like this tend to overachieve rainfall wise, and that will likely
be the case this time as well. Thus we still tend to think the new
00z HREF guidance is too dry (with the PMM suggesting localized
totals of ~1.5"), and there may still be an uptick in model QPF in
future runs (with totals in vicinity of one of the wetter models,
the 00z GEM-Reg, still quite possible). Overall, not anticipating
a significant flash flood threat, but localized, mainly urban,
flash flooding is a possibility.

Churchill/Chenard


Day 2
Valid 12Z Tue Mar 04 2025 - 12Z Wed Mar 05 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE UPPER MIDWEST AND PORTIONS OF THE MID-SOUTH INTO THE SOUTHEAST...

A pattern change will bring widespread precipitation to much of the
Central and Southeast CONUS, as a cut-off low/upper-level trough
and associated surface cyclone progress across the middle portion
of the country. QPF maxima continue to be expected across two
general regions, in and around the Mid-South (primarily in
associated with precipitation from the broad open warm sector and
subsequent cold frontal passage) and much of IA into northern MO
(mainly from the pivoting low pressure center as it occludes).
While flash flood impact coverage should remain somewhat limited in
both areas (low-end Slight risk probabilities) with relatively dry
antecedent conditions and a rather progressive storm system
motion, the very dynamic nature of the system is still likely to
bring periods of strong convection with localized totals nearing
2". While a portion of the QPF over IA is likely to be in the form
of snow on the back-end of the low, the expected 2" total will also
be relatively long duration, as rates will be limited to 0.5"/hr
with a relative lack of instability. Over the Mid-South and
Southeast, any localized 2" totals could occur over a much shorter
period of time (as little as an hour) as instability which be much
more plentiful. Barring any major changes in the forecast strength
and progression of the storm system, impacts are likely to be
capped at the Slight threshold with continued refinement to the
outlook with the addition of more CAM data over the next day or so.

Churchill


Day 3
Valid 12Z Wed Mar 05 2025 - 12Z Thu Mar 06 2025

...A MARGINAL RISK OF EXCESSIVE RAINFALL EXISTS FOR PORTIONS OF
SOUTHERN CALIFORNIA AND THE NORTHEAST...

...Southern California...
A cyclone moving towards the region at the base of an amplifying
and progressive West Coast upper level trough brings precipitable
water values near the coastal ranges above 1", with 0.75"+
extending into the deserts. While the strength of the low-level
inflow is modest -- 25+ kts -- the system has some instability to
work with which could allow for hourly rain totals to reach 0.5",
which would be most problematic in burn scars. Overall totals
appear to be capped near 3". The inherited Marginal Risk appears
reasonable, so changes to the area depicted were minimal.

...Northern Mid-Atlantic States/Southern New England...
A progressive deep layer cyclone moves through the Great Lakes into
Southeast Canada, bringing of shot of 60 kt inflow at 850 hPa into
the region with precipitable water values rising to 1-1.25".
Portions of PA, NY, and the southern coast of New England appear
to have some instability to work with, as MU CAPE of 250-500 J/kg
is forecast to be available. Along with low- to mid-level
frontogenesis, hourly rain totals to 1.25" should be possible.
While most of this area has had below average precipitation this
past week, a good portion of New England north of CT/RI/southeast
MA have 1-2" of snow water equivalent on the ground, so melting
snow should be occurring as well considering the strength of the
warm air advection which could raise both temperatures and dew
points well into the 40s. The inherited Marginal Risk both fits
the most recent QPF guidance and the ideas above, so changes to the
area depicted were minimal.

Roth

$$
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FOUS30 KWBC 040748
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
248 AM EST Tue Mar 4 2025

Day 1
Valid 12Z Tue Mar 04 2025 - 12Z Wed Mar 05 2025

..THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM PORTIONS OF
THE CORN BELT INTO THE ARKLATEX...

A deep layer cyclone progresses across the middle portion of the
country, drawing in moisture and instability from the south. QPF
maxima stretch between two general regions, in and around the
ArkLaTex (primarily with a squall line which could have a LEWP/QLCS
character at times and preceding isolated to scattered convection
which could merge into the line) and much of IA into northern MO
(mainly from the pivoting low pressure center as it occludes).
While flash flood impact coverage should remain somewhat limited in
both areas (a lower end Slight risk probability) with relatively
dry antecedent conditions and a rather progressive storm system
motion, the dynamic nature of the system is likely to bring periods
of strong convection with hourly rain totals to 2" and localized
storm totals nearing 3". While a portion of the QPF over IA is
likely to be in the form of snow on the back-end of the low, the
expected 3" total will also be relatively long duration, as rates
will be limited to 0.5"/hr with a relative lack of instability for
northern areas of the Slight Risk. The main change this update was
to link together the Slight Risk areas.

Over the Southeast, the bigger problem spot appears the be the
southern Appalachians as Atlantic and Gulf fetches maintain
moisture/stronger low-level inflow longer than other areas of the
region. The 00z HREF probabilities of 3"+ are above 50%, with non-
zero probabilities of 5"+ amounts. The area has been dry as of
late, so antecedent conditions suggest that some degree of this
rainfall would be beneficial. Capped the risk as a Marginal for
now, after coordination with GSP/the Greer SC forecast office,
though it is a high end Marginal Risk for the southern Appalachians.

Roth/Churchill


Day 2
Valid 12Z Wed Mar 05 2025 - 12Z Thu Mar 06 2025

...A MARGINAL RISK OF EXCESSIVE RAINFALL EXISTS FOR PORTIONS OF
SOUTHERN CALIFORNIA AND THE NORTHEAST...

...Southern California...
A cyclone moving towards the region at the base of an amplifying
and progressive West Coast upper level trough brings precipitable
water values near the coastal ranges above 1", with 0.75"+
extending into the deserts. The strength of the low-level inflow
has weakened from what was seen in the guidance from 24 hours ago,
except in eastern sections of the Transverse Ranges, the
Peninsular Ranges, and upslope areas of the Sierra Nevada. The
system has some instability to work with which could allow for
hourly rain totals to reach 0.5", which would be most problematic
in burn scars. Overall totals appear to be capped near 3". The
inherited Marginal Risk was pared back a bit across the western
Transverse Ranges and coastal ranges north of Lompoc from continuity.

...Northern Mid-Atlantic States/Southern New England...
A progressive deep layer cyclone moves through the Great Lakes into
Southeast Canada, bringing of shot of 60 kt inflow at 850 hPa into
the region with precipitable water values rising to 1-1.25".
Portions of PA, NY, and the southern coast of New England appear
to have some instability to work with, as MU CAPE of 250-500 J/kg
is forecast to be available. Along with low- to mid-level
frontogenesis, hourly rain totals to 1.25" should be possible.
While most of this area has had below average precipitation this
past week, a good portion of New England north of CT/RI/southeast
MA have 1-2" of snow water equivalent on the ground, so melting
snow should be occurring as well, considering the strength of the
warm air advection which could raise both temperatures and dew
points well into the 40s. The inherited Marginal Risk both fits
the most recent QPF guidance and the ideas above, so changes to the
area depicted were minimal.

Roth


Day 3
Valid 12Z Thu Mar 06 2025 - 12Z Fri Mar 07 2025

...A MARGINAL RISK OF EXCESSIVE RAINFALL EXISTS FOR PORTIONS OF
SOUTHERN CALIFORNIA...

...Southern California...
Sufficient low-level inflow from the Pacific, as high as 40 kts or
so, combined with small amounts of instability and precipitable
water values of 0.5-0.75" appear sufficient for hourly rain totals
to rise towards 0.5" an hour, so left the Marginal Risk from
continuity reasonably intact. It is expected to be the relatively
cold atmosphere, so heavy snow is possible within the risk area in
the higher peaks. The main flash flood risk would be to areas with
burn scars.

Roth

$$
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FOUS30 KWBC 050743
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
243 AM EST Wed Mar 5 2025

Day 1
Valid 12Z Wed Mar 05 2025 - 12Z Thu Mar 06 2025

...A MARGINAL RISK OF EXCESSIVE RAINFALL EXISTS FOR PORTIONS OF
SOUTHERN CALIFORNIA, NORTHEAST, AND MID-ATLANTIC...

...Mid-Atlantic States through New England...

Potent mid-latitude cyclone over the Midwest will progress further
into the Great Lakes during the period with a strong southerly
moisture advection regime located over the Eastern CONUS. Fairly
textbook meridional push of warm, unstable air will press northward
amidst a potent 850-700mb layer of winds between 60-80kts with PWAT
anomalies pushing the 95-99th percentiles extending from the
Carolinas all the way into Southern New England. Sharp cold front
pivoting underneath the primary cyclone will press eastward through
the Southeastern U.S with the fronts northern latitudinal placement
shifting through the Mid-Atlantic and Northeast. The combination of
deep layer moisture, modest theta_E advection, and strong
surface/low-level convergence will create a relatively progressive
line of convection later this morning over Appalachia, moving
eastward through the Piedmont creating a period of heavy rain
potential within the urban corridors extending from Philadelphia to
the Triad of North Carolina. Area FFGs are most prone to flood
prospects within the DC/Balt, Richmond, and Philadelphia metros
with the Raleigh-Durham corridor signaling a much higher threshold
which should limit the potential despite the convective signature present.

00z HREF neighborhood probs for >1" are very high (80%) over much
of the Mid-Atlantic and Northeast, but probs for >2" are much more
muted outside some spots within the Blue Ridge of VA up through PA.
The urbanization factors will create the greatest prospects for
localized flash flood concerns, especially given the 1-2"/hr rates
anticipated as the primary axis of convection blows through during
the afternoon. Southeastern VA across the Hampton Roads area will
be another area of concern with much of the latest CAMs output
fairly aggressive for the local 1-2" totals over a very short span
of time. Considering the heightened risk for this area due to the
urbanization factors, the previous MRGL risk was extended south and
southeast to include those places like Norfolk/VA Beach within the
Tidewater, as well as the Richmond metro where hi-res depictions
for heavy rainfall within a corridor of greater instability is
increasingly likely. Further north into New England, heavy rainfall
coupled with snow melt will allow for greater flood concerns, along
with ice jam concerns coupled with the rain over portions of
Downeast ME. The previous MRGL issuance was relatively unchanged in
those areas with the biggest addition focused over VA and Southern MD.

...Southern California...

Troughing over the Eastern PAC will make headway into the West
coast with sights on CA as we move through period. A formidable
moisture advection pattern is forecast across Central and Southern
CA with the strongest anomalies (95-99th percentiles) focused over
the Southern CA terrain thanks to prevailing southwesterly flow
providing a but of an orthogonal component to the wind field.
PWATs will be generally between 0.75-1" with locally higher within
the confines of the coast. This is generally an output that puts
the coastal terrain within the LA and San Diego domains at risk for
localized flash flood concerns normally due to the complexity of
the terrain. We add in the positioning of several major burn scars
lingering over the Transverse and Peninsular Ranges and you create
a better opportunity for those flood concerns, especially
considering the threshold is hovering ~0.5"/hr at best. Thankfully
the rates will be mainly relegated to the 0.5-1"/hr at peak
intensity during the height of impacts this evening. This was
enough to warrant a continuation of the previous MRGL in place with
an extension to the Southern Sierra Foothills where heavy precip
totals between 2-3" are forecast within complex terrain just east
of the Valley.

Kleebauer


Day 2
Valid 12Z Thu Mar 06 2025 - 12Z Fri Mar 07 2025

...A MARGINAL RISK OF EXCESSIVE RAINFALL EXISTS FOR PORTIONS OF
SOUTHERN CALIFORNIA...

Persistent in-flow trailing the mean trough propagating into the
Western CONUS will allow for continued moderate precip in-of the
Southern California terrain, mainly the Transverse and Peninsular
ranges within the Los Angeles and San Diego WFO domains. Areal
moisture flux will be trending down in terms of anomalies with the
highest PWATs centered further inland. Despite the evolution in
question, this is mainly a continuation from the period prior
leading to ongoing flash flood potential within the terrain where
several burn scars are present. Fortunately, the setup degrades
further by the second half of the period, leading to mainly
scattered shower instances as we move into the overnight period
Thursday through early Friday morning. Majority of guidance has
precip between 0.5-1" within the mountains outside LA and San
Diego, enough to continue any flood prospects that occurs on D1.
The previous MRGL was relatively unchanged as guidance maintains
run-to-run continuity.

Kleebauer


Day 3
Valid 12Z Fri Mar 07 2025 - 12Z Sat Mar 08 2025

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

Kleebauer

$$
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FOUS30 KWBC 060754
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
254 AM EST Thu Mar 6 2025

Day 1
Valid 12Z Thu Mar 06 2025 - 12Z Fri Mar 07 2025

...A MARGINAL RISK OF EXCESSIVE RAINFALL EXISTS FOR PORTIONS OF
SOUTHERN CALIFORNIA...

Trailing vorticity maxima analyzed off the coast of CA will rotate
around the backside of the mean trough ejecting into the
Southwestern U.S. A slight void in precipitation, outside some
lingering showers will transpire this morning as the primary ascent
focuses further inland. A trailing mid-level shortwave will motion east-southeastward into the southern portion of CA later this
afternoon and evening with one last enhancement for scattered to
widespread convection as the energy accompanies a more focused
850-700mb moisture flux as progged. The heaviest precip time frame
will likely occur as the nose of the 700mb jet moves ashore near
San Diego with the streaming westerlies working inland with low-
level ascent maximized over the southern end of the Transverse
Range down through the Peninsular Range just east of San Diego proper.

Latest CAMs output is pretty consistent with the areal max hovering
between 1-2" across the above locations with the highest situated
closer to the Baja border just east of the SD metro. This is mainly
due to the forecast orientation of the 700mb jet co-located within
this small zone, a consistency among most of the deterministic
suite this evening. PWATs will be generally near to just above
seasonal for the anomalies (0.6-0.9"), but considering the previous
period of rainfall with remnant burn scars being impacted
currently, the continued rainfall will only maintain the potential
for low-end flash flood exceedance. With the 00z HREF
EAS/neighborhood probs nestled between 70-90% for at least 1" over
the hardest hit locations in the Peninsular/Transverse domain, a
continuation of the MRGL risk was still relevant given the
characteristics above.

Kleebauer


Day 2
Valid 12Z Fri Mar 07 2025 - 12Z Sat Mar 08 2025

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

Kleebauer


Day 3
Valid 12Z Sat Mar 08 2025 - 12Z Sun Mar 09 2025

...A MARGINAL RISK OF EXCESSIVE RAINFALL EXISTS FOR PORTIONS OF THE
CENTRAL GULF COAST...

A fairly robust upper-low over the Southwestern U.S will pivot
eastward into the Southern Plains with multiple shortwave ejections
crossing out of the Gulf with steady motion through the Gulf coast.
The proxy of the dynamic upper pattern will help initiate surface
cyclogenesis in-of the Gulf coast with most deterministic now
developing a surface low just south of LA by the end of the D3 time
frame. Southerly flow ahead of the mean trough will lead to the
advection of more warm, moist air northward with the northern
fringe notated by a developing warm front that is depicted when
assessing the sfc-850mb wind field showing convergent flow in-of
the boundary. Guidance is becoming more focused along the Gulf
coast for the proxy of the boundary which will be key in
determining the northern extent of the instability field which will
be situated south of the aforementioned front.

Trends within most of the deterministic and ensembles have now
shifted further south with the heaviest QPF footprint, aligning
with the ML guidance over the past 24 hrs that place the more
significant theta_E tongue within the proximity of the Gulf coast
area extending from southeastern LA over into the FL Panhandle.
PWAT anomalies are pushing towards the +2 deviation marker, a
threshold typically necessary this time of year to attain any flash
flood threat due to the locally elevated FFG's within this area of
the CONUS. Ensemble output of 1-3" is focused within the corridor
extending from the Southeastern most Parishes of LA through the
I-10 corridor, including places like Mobile, Pensacola, Panama
City to as far east as Tallahassee. The ECMWF has been the most
consistent with this forecast over the past several runs with the
other global deterministic slowly shifting south with the primary
axis of heavier QPF. Considering the better instability gradient
closer to the Gulf coast, the best chance for heavier convection
will likely lie in that warm sector south of the warm front, and
within the convergent axis just inland within the bounds of the
front placement. Steering flow is likely to align parallel to the
front as the west-east placement will create a funneling affect for
moisture within that zone of expected impact.

The previous MRGL risk was trimmed on the northern and western
extent and now encompasses a smaller region along the Central Gulf
Coast, including the cities referenced above. This was also agreed
upon by the local MOB/TAE WFO's representing the areas in question.
Will assess the trends closely in the coming days, but the
prospects flash flooding remain in reason to maintain some
continuity.

Kleebauer

$$
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FOUS30 KWBC 070844 AAA
QPFERD

Excessive Rainfall Discussion...UPDATED
NWS Weather Prediction Center College Park MD
344 AM EST Fri Mar 7 2025

Day 1
Valid 12Z Fri Mar 07 2025 - 12Z Sat Mar 08 2025

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

Bann


Day 2
Valid 12Z Sat Mar 08 2025 - 12Z Sun Mar 09 2025

...A MARGINAL RISK OF EXCESSIVE RAINFALL EXISTS FOR PORTIONS OF THE
CENTRAL GULF COAST...

There will be an increasing chance for showers and thunderstorms to
organize and become capable of producing rainfall rates in the 1 to
2 inch per hour range along portions of the central Gulf coast on
Saturday and Saturday night.

A fairly potent upper low will be making its way from the Southwest
U.S. into the Southern Plains by early Sunday morning. South to
southwesterly low level flow ahead of the mid- level energy will
start to draw moisture northward...with precipitable water values
increasing into the range between 1.50 and 1.75 inches by Saturday afternoon...although present indications are that the higher
rainfall rates probably do not develop until the better upper level
support arrives and a well- defined cold front makes approaches
the coast later in the day.

The 07/00Z suite of QPF guidance still focused parts of the Gulf
coast for mainly a low-end risk of excessive rainfall...which mirrored
the WPC deterministic QPF preference which gave least
consideration to the more northerly position of the GFS QPF
compared with other operational model runs...and offered strong
support to the placement of yesterday's Day 3 ERO.
Consequently...only minor changes were needed.

Bann


Day 3
Valid 12Z Sun Mar 09 2025 - 12Z Mon Mar 10 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE SOUTHEAST U.S....

The potent shortwave trough that brings the risk of excessive
rainfall along the Gulf coast on Day 2 will continue tracking
eastward from the Southern Plains towards the Florida panhandle or
southern Alabama by early Monday morning.. Moist southwesterly
flow ahead of the system will have drawn an airmass with
precipitable water values in excess of 1.5 inches over portions of
the northern Florida peninsula and adjacent parts of Georgia. The
WPC deterministic QPF forecaster still gave less weight to the
GFS...resulting in little need to make more than some cosmetic
changes to the placement of yesterday's Day 4...before the bulk of
the rainfall from this system moves offshore.

Bann

$$
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FOUS30 KWBC 080822
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
322 AM EST Sat Mar 8 2025

Day 1
Valid 12Z Sat Mar 08 2025 - 12Z Sun Mar 09 2025

...A MARGINAL RISK OF EXCESSIVE RAINFALL EXISTS FOR PORTIONS OF THE
CENTRAL GULF COAST...

19Z Update...
No significant changes were made to the previous outlook area.

Previous discussion...
There will be an increasing chance for showers and thunderstorms
capable of producing localized downpours later today and tonight
across portions of the central Gulf coast. There could be some
rainfall rates that exceed one inch per hour as a fairly potent
shortwave trough/upper low makes its way from the Southwest U.S.
into the Southern Plains by early Sunday morning. South to
southwesterly low level flow ahead of the mid- level energy will
start to draw moisture northward...with precipitable water values
increasing into the range between 1.50 and 1.75 inches by later
this afternoon...although model guidance still suggests that the
higher rainfall rates probably do not develop until the better
upper level support approaches and a well-defined cold front nears
the coast later tonight/early Sunday morning, Given the Flash Flood
Guidance in the region...not expecting more than isolated problems
given the 08/00Z HREF neighborhood probabilities for amounts
exceeding an inch of accumulation in one hour.

Bann


Day 2
Valid 12Z Sun Mar 09 2025 - 12Z Mon Mar 10 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE SOUTHEAST U.S....

Considerable spread remains in the numerical guidance in term of placement...but enough QPF along the path of a well-defined
shortwave to keep a Marginal risk in place. The 08/00Z GFS
started out in fairly good agreement with other models but becomes
a northerly outlier as it gets drawn northward by northern stream energy...while the 08/00Z NAM continued to indicate heavier
rainfall with a greater threat for flash flooding farther north.
Less weight for now was given to these solutions, keeping the
deterministic QPF and the Marginal Risk for excessive rainfall more
in line with the more southerly ECMWF, CMC, and UKMET guidance. In
large part...there were few changes needed given good continuity
with the WPC deterministic QPF and the consensus QPF of the non-
NCEP guidance.

Bann


Day 3
Valid 12Z Mon Mar 10 2025 - 12Z Tue Mar 11 2025

The probability of rainfall exceeding Flash Flood Guidance is less
than 5 percent.

Bann

$$
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FOUS30 KWBC 090835
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
435 AM EDT Sun Mar 9 2025

Day 1
Valid 12Z Sun Mar 09 2025 - 12Z Mon Mar 10 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE SOUTHEAST UNITED STATES...

Have introduced a Slight Risk area from the Florida panhandle
eastward into portions of the northern Florida peninsula and
adjacent portions of southern Georgia given increasing support
from the models...both global and mesoscale...for higher rainfall amounts/rates.

Present indications are that convection capable of producing
rainfall rates in excess of an inch per hour will be possible in a
corridor along/near the coastal portions of the Florida panhandle
northeastward from this morning into early afternoon (approximately
in the period from 12Z to 18Z) in association with one shortwave
that taps some Gulf instability. Another round of moderate to heavy
rainfall looks to develop in the 10/00Z to 10/06Z period as a
second shortwave follows a similar path as the first shortwave.
Rainfall totals in of 2 to 4 inches could occur within that
corridor...although there could easily be some higher amounts
embedded within the belt of heavy rainfall. Those rainfall amounts
have the potential to result in flooding of low-lying areas, creeks
and roadways.

Bann


Day 2
Valid 12Z Mon Mar 10 2025 - 12Z Tue Mar 11 2025

The probability of rainfall exceeding Flash Flood Guidance is less
than 5 percent.

Bann


Day 3
Valid 12Z Tue Mar 11 2025 - 12Z Wed Mar 12 2025

The probability of rainfall exceeding Flash Flood Guidance is less
than 5 percent.

Bann

$$
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FOUS30 KWBC 100720
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
320 AM EDT Mon Mar 10 2025

Day 1
Valid 12Z Mon Mar 10 2025 - 12Z Tue Mar 11 2025

The probability of rainfall exceeding Flash Flood Guidance is less
than 5 percent.

Chenard


Day 2
Valid 12Z Tue Mar 11 2025 - 12Z Wed Mar 12 2025

The probability of rainfall exceeding Flash Flood Guidance is less
than 5 percent.

Chenard


Day 3
Valid 12Z Wed Mar 12 2025 - 12Z Thu Mar 13 2025

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

A deep mid level trough and cold front will move across CA
Wednesday into Wednesday night bringing widespread rain and
mountain snow to the region. The IVT axis is rather narrow and
quick moving and only forecast to peak around 400-600
kg/m/s. When combining this modest strength and lack of longevity
of these higher values...this event will likely only reach weak
atmospheric river levels. This limitation will be partially offset
by the strength of the cold front and deep layer forcing
associated with the synoptic scale trough and upper jet. Even so,
rainfall totals over much of the state are unlikely to be enough to
cause much of a flood concern. Mainly looking at a beneficial
rainfall, although some locally higher rates near the front could
be enough to result in generally minor and localized flooding
within urban and other prone low lying areas.

More flood impacts are possible over southern CA, specifically
portions of Santa Barbara, Ventura and Los Angeles counties. South
to southwesterly upslope flow into the Transverse range will likely
help enhance rainfall over this area late Wednesday night into
Thursday morning. Also will likely have a bit better large scale
forcing overrunning the front at the base of the mid level trough,
helping steepen lapse rates and increasing rainfall rate potential.
Most of the weak instability is currently forecast to be post-
frontal, but could see just enough destabilization work into the
front to produce some localized convective elements within the
southward shifting rainfall axis. It does seem probable that some
0.5"/hr rainfall will accompany this front, and while any heavy
rates will only last for an hour or two, this could be enough to
locally increase the flash flood threat over the more sensitive
burn scars and any flood prone urban areas. The quick shot of
potential high rainfall rates, combined with the sensitive burn
scars over this area, warrants a Slight risk upgrade, and localized
significant impacts are possible.

Chenard

$$
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FOUS30 KWBC 110756
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
356 AM EDT Tue Mar 11 2025

Day 1
Valid 12Z Tue Mar 11 2025 - 12Z Wed Mar 12 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF SOUTHERN CALIFORNIA...

A deep layered low moving into southern CA will bring showers, and
even possibly an isolated thunderstorm, to the region today into
this evening. Showers will initially be on the lighter side,
however as the center of the low approaches steeper lapse rates
will support some modest destabilization and an uptick in shower
intensity between approx 21z-03z. The 00z HREF neighborhood
probability of exceeding 0.5" in an hour peaks between 60-70% just
offshore, with hourly rainfall even exceeding 0.75" in this
offshore activity. These stronger showers and isolated
thunderstorms will likely weaken as they move onshore...however
expect that hourly rainfall will still approach or exceed 0.5" on a
localized basis over land as well. Overall expecting total
rainfall amounts between 0.5" and 1" on a pretty widespread basis
over far southern CA, with localized totals of 1-2". These totals,
combined with the locally higher rates expected, support a
generally minor and localized flood risk today...mainly across any
more sensitive urban areas and/or sensitive terrain.

Chenard


Day 2
Valid 12Z Wed Mar 12 2025 - 12Z Thu Mar 13 2025

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

The forecast generally remains on track, so only minimal changes
needed to the risk areas with this update. A deep mid level trough
and cold front will move across CA Wednesday into Wednesday night
bringing widespread rain and mountain snow to the region. The IVT
axis is rather narrow and quick moving and only forecast to peak
around 400-600 kg/m/s. When combining this modest strength and lack
of longevity of these higher values...this event will likely only
reach weak atmospheric river levels. This limitation will be
partially offset by the strength of the cold front and deep layer
forcing associated with the synoptic scale trough and upper jet.
Even so, rainfall totals over much of the state are unlikely to be
enough to cause much of a flood concern. Mainly looking at a
beneficial rainfall, although this is a strong cold front with a
well defined convergence axis along it, and this could drive some
locally higher rainfall rates, both along the coast and within the
Sacramento Valley where southerly flow could locally enhance
convergence further. These higher rates could be enough to result
in generally minor and localized flooding within urban and other
prone low lying areas.

More flood impacts are possible over southern CA, specifically
portions of Santa Barbara, Ventura and Los Angeles counties. South
to southwesterly upslope flow into the Transverse range will likely
help enhance rainfall over this area late Wednesday night into
Thursday morning. Also will likely have a bit better large scale
forcing overrunning the front at the base of the mid level trough,
helping steepen lapse rates and increasing rainfall rate potential.
Most of the weak instability is currently forecast to be post-
frontal, but could see just enough destabilization work into the
front to produce some localized convective elements within the
southward shifting rainfall axis.

We will likely get a better idea on peak rainfall rate potential
when the 12z HREF arrives today...however the 00z 3km NAM
indicates hourly rates over 0.5" and 3 hourly rainfall of 1-2". The
GEM reg has also shown some skill in past southern CA events at
depicting max rainfall potential...and it peaks at just over 2" in
3 hours between 06z and 12z. Thus still thinking hourly rainfall
peaking between 0.5" and 0.75" is likely, particularly within areas
of terrain. Although even along coastal areas convective elements
near the front could locally push rates towards 0.5" in an hour.
This is a quick moving system, and thus these elevated rates should
only last at most a few hours, but this could be enough to locally
increase the flash flood threat over the more sensitive burn scars
and any flood prone urban areas. Thus a Slight risk remains
warranted and localized significant debris flows are possible.

Chenard


Day 3
Valid 12Z Thu Mar 13 2025 - 12Z Fri Mar 14 2025

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

The event described in the day 2 discussion will be ongoing at 12z
Thursday over southern CA. Rainfall rates locally over 0.5" an
hour will remain possible along the southward moving cold front
between 12z and 18z. The front will remain fast moving, so the
flood risk should be over by 18z. The IVT magnitudes generally are
sustained through Thursday morning and the approach the the mid
level trough axis and shortwave energy at the base of the trough
should help enhance synoptic ascent over the front. Thus expect
the area of showers and embedded heavier convective elements to
generally maintain intensity as it drops through far southern CA.
Rainfall amounts of 1-3" are possible in the terrain, with even
0.75"-1.5" across lower elevations. This should be enough to
maintain a flood risk across this region, with sensitive urban
areas and burn scars most susceptible to flood impacts. Rainfall
on day 1 (Tuesday) may be enough to increase soil saturation and
streamflows, which could result in a bit more coverage of impacts
with this 2nd system Thursday morning. Given these factors, we went
ahead and upgraded to a Slight risk over this region.

Chenard

$$
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FOUS30 KWBC 120759
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
359 AM EDT Wed Mar 12 2025

Day 1
Valid 12Z Wed Mar 12 2025 - 12Z Thu Mar 13 2025

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

The forecast generally remains on track, so only minimal changes
needed to the risk areas with this update. The greatest flood risk
with this event remains over southern CA Wednesday evening into
Thursday morning. The 00z HREF continues to indicate a high
probability of hourly rainfall locally exceeding 0.5" moving into
the Transverse Range of Santa Barbara and Ventura counties as early
as ~04z, and then spreading into the San Gabriel Mountains of Los
Angeles county closer to 08z. While the probability of 0.5"+ an
hour hourly rainfall is high, the coverage of these more intense
rates will likely be localized in nature, as shown by the HREF 0.5"
per hour ensemble agreement scale probabilities (more of an
indication of coverage) which peak in the 10-15% range over the
aforementioned terrain areas.

Most of the 00z CAMs indicate a narrow line of shallow convection
moving south across these areas associated with strong cold
frontal convergence and about 100-200 j/kg of CAPE. This feature,
combined with orographic enhancement, should locally push hourly
rainfall into the 0.5" to 0.75" range over the aforementioned
terrain of Santa Barbara, Ventura and Los Angeles counties. Rates
should tend to be a bit lower outside of the terrain, although the
shallow convective line could locally push hourly rainfall over
0.5" even along lower elevation coastal areas. This axis of heavier
rain will be quick moving and only last about 2-3 hours at any one location...which will limit total rainfall amounts and the
magnitude/coverage of the flash flood threat. However, even with
the quick movement, rainfall rates could be high enough to result
in locally significant flood impacts near recent burn scars, and
areas of minor flooding in other more flood prone urban or low lying areas.

Elsewhere across the state of CA the deep mid level trough and
cold front will bring widespread rain and mountain snow to the
region. The IVT axis is rather narrow and quick moving and only
forecast to peak around 400-600 kg/m/s. When combining this modest
strength and lack of longevity of these higher values...this event
will likely only reach weak atmospheric river levels. This
limitation will be partially offset by the strength of the cold
front and deep layer forcing associated with the synoptic scale
trough and upper jet. Even so, rainfall totals over much of the
central and northern CA are unlikely to be enough to cause much of
a flood concern. Mainly looking at a beneficial rainfall, although
this is a strong cold front with a well defined convergence axis
along it, and this could drive some locally higher rainfall rates,
both along the coast and within the Sacramento Valley where
southerly flow could locally enhance convergence further. These
higher rates could be enough to result in generally minor and
localized flooding within areas of steep terrain along with urban
and other prone low lying areas.

Chenard


Day 2
Valid 12Z Thu Mar 13 2025 - 12Z Fri Mar 14 2025

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

The event described in the day 2 discussion will be ongoing at 12z
Thursday over southern CA. A shallow convective line along the
cold front will continue to support rainfall rates locally over
0.5" between 12z and 15z, with the quick frontal motion meaning
most of the higher rates should abate after 15z. The IVT
magnitudes generally are sustained through Thursday morning and the
approach the the mid level trough axis and shortwave energy at the
base of the trough should help enhance synoptic ascent over the
front. Thus expect the area of showers and embedded heavier
convective elements to generally maintain intensity as it drops
through far southern CA, and this is supported by the 00z HREF.

While rainfall totals will likely be higher in the terrain where
upslope flow enhances ascent, the southward dropping line of
shallow convection should support rainfall rates locally over 0.5"
an hour even over coastal areas. These higher rates (albeit brief)
support some flood risk over this region, with sensitive urban
areas and burn scars most susceptible to flood impacts. While
rainfall on Tuesday averaged only between 0.25"-0.75", the
resulting modest soil saturation and streamflow increase could
still play a factor in locally increasing impacts when this next
round of heavier rates moves through early Thursday.

Chenard


Day 3
Valid 12Z Fri Mar 14 2025 - 12Z Sat Mar 15 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
LOWER TO MIDDLE MISSISSIPPI VALLEY INTO PORTIONS OF THE OHIO AND
TENNESSEE VALLEY...

A strong mid level low and shortwave energy ejecting east out of
the Plains and into the MS Valley will likely trigger strong to
severe convection by Friday afternoon across portions of MO, AR and
IA. This activity will then spread eastward into portions of IL,
IN, KY, TN and MS Friday evening into the overnight hours. Moisture
is initially quite limited with this system although we eventually
see a narrow corridor of higher PWs advect northward. Cell motions
are also likely going to be quite fast off to the east northeast
given the very strong wind fields in place. Thus this convection
will likely pose more of a severe risk than it will a flash flood
risk. However this is a very dynamic system with sufficient
instability for deep convection, and so expect that rainfall rates
will briefly be intense enough that we will see swaths of rainfall
that exceed current model forecasts (maybe locally over 2").
Nonetheless, this still appears to be a lower end flood threat, and
probably confined to localized impacts over any more sensitive
urban or low lying areas that pick up a quick burst of intense
rainfall rates.

The southern end of the Marginal risk over MS will see an uptick
in convection Saturday morning. The front should slow/stall over
this region with shortwave energy approaching within the base of
the longwave trough helping enhance moisture transport and large
scale ascent. Most models suggest an uptick in the flash flood risk
from possible training convection in the 12z-18z Saturday
timeframe (so just after this day 3 period), but can not rule out
some impacts beginning just before 12z, as these events can often
grow upscale a bit earlier than forecast.

Chenard

$$
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FOUS30 KWBC 130800
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
400 AM EDT Thu Mar 13 2025

Day 1
Valid 12Z Thu Mar 13 2025 - 12Z Fri Mar 14 2025

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

A strong Pacific cold front associated with an amplified upper
trough will continue to drop southeastward along the southern
California coast this morning. Hi-res guidance indicates that
moisture advection and modest instability ahead of the front will
be sufficient to maintain rainfall rates of 0.5+ in/hr along the
coast into the upslope areas of the Peninsular Ranges early in the
period. Rates are expected to diminish as the front moves south
and east into the Colorado Basin and the Baja Peninsula by late
morning, but not before an additional 1-2 inches of rain falls
across portions of the highlighted area. Neighborhood probabilities
indicate the greatest threat for heavier amounts is centered along
along the orographically favored regions of the Peninsular Ranges.
A Slight Risk was maintained for areas at or below 3500 ft, where
precipitation is expected to fall as mostly or all rain.

Pereira


Day 2
Valid 12Z Fri Mar 14 2025 - 12Z Sat Mar 15 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE LOWER TO MID MISSISSIPPI VALLEY INTO PARTS OF THE OHIO AND
TENNESSEE VALLEYS...

A strong mid-to-upper level shortwave crossing the Southwest on Day
1 is expected to move east of the Rockies, with a negatively-tilted
low developing over the central Plains early in the period.
Powerful forcing is forecast to interact with what is expected to
be a relatively modest plume of moisture advecting north ahead of
the system. Storms are forecast to develop initially over the
lower to mid Mississippi Valley Friday afternoon before moving
east into the Tennessee and Ohio valleys during the evening and
overnight. Cell motions will likely be quite progressive given the
very strong wind fields in place. Therefore, this convection will
likely pose more of a severe risk than a flash flood threat.
However, given the strong dynamics, along with sufficient
instability for deep convection, expect that rainfall rates will be
briefly intense enough to produce localized amounts that exceed
current model forecasts (maybe locally over 2 inches).
Still, this appears to be a lower-end flood threat, and probably
confined to localized impacts over more sensitive urban or low
lying areas that are impacted by a quick burst of intense rainfall.

Pereira


Day 3
Valid 12Z Sat Mar 15 2025 - 12Z Sun Mar 16 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
TENNESSEE AND OHIO VALLEYS...

Even as the previously noted low lifts to the north through the
Great Lakes into Ontario, the upper pattern will remain amplified
across the central U.S. as an upstream shortwave dives southeast
into the southern Plains on Saturday. A surface wave developing
along the leading system's trailing cold front will help focus
deeper moisture tapped by strengthening southerly winds. While
differences in the details remain, the general consensus of the 00Z
guidance indicates that widespread accumulations of 2-4 inches
centered over parts of the Tennessee and lower Ohio Valleys are
likely. A large Slight Risk was maintained across the region,
reflecting the higher probabilities for 2 inches or more shown by
by the GEFS/ECENS and where deeper moisture, interacting with
strong forcing, along a relatively slow moving front, is expected
to raise the potential for heavy amounts late Saturday
into early Sunday. This remains a higher-end Slight Risk for parts
of the area, with an upgrade to a Moderate Risk possibly
forthcoming, especially once the period moves within the hi-res
window and details concerning rainfall rates and the placement of
the heaviest amounts become more clear.

Pereira

$$
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FOUS30 KWBC 140810
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
410 AM EDT Fri Mar 14 2025

Day 1
Valid 12Z Fri Mar 14 2025 - 12Z Sat Mar 15 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE LOWER TO MID MISSISSIPPI VALLEY INTO PARTS OF THE OHIO AND
TENNESSEE VALLEYS...

A strong mid-to-upper level shortwave currently crossing the
Southwest will move east of the Rockies today, with a negatively-
tilted low developing over the central Plains early in the period.
Powerful forcing is forecast to interact with a relatively modest
plume of moisture advecting north ahead of the system. Storms are
expected to develop initially over the lower to mid Mississippi
Valley this afternoon before moving east into the Tennessee and
Ohio valleys during the evening and overnight. Cell motions will be
quite progressive given the very strong wind fields in place.
Therefore, this convection will almost certainly pose more of a
severe risk than a flash flood threat. However, given the strong
dynamics, along with sufficient instability for deep convection,
expect peak rainfall rates will be briefly intense enough
(~1-2"/hr) to produce localized amounts that exceed current model
forecasts (2-3 inches over relatively short period). Still, this
appears to be a lower-end flood threat, and probably confined to
localized impacts over more sensitive urban or low lying areas that
are impacted by a series of 2-3 training cells in a short period.

Churchill/Pereira


Day 2
Valid 12Z Sat Mar 15 2025 - 12Z Sun Mar 16 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
TENNESSEE AND OHIO VALLEYS...

...Ohio and Tennessee Valleys...

Even as the previously noted low lifts to the north through the
Great Lakes into Ontario, the upper pattern will remain amplified
across the central U.S. as an upstream shortwave dives southeast
into the southern Plains on Saturday morning and spreads eastward
over the Lower Mississippi Valley into Saturday afternoon/evening.
A surface wave developing along the leading system's trailing cold
front will help focus deeper moisture tapped by strengthening
southerly winds and with increasing upper-level dynamical support
as the southern shortwave approaches. This will help lead to the
continued development and maintenance of an intense line of
thunderstorms pushing eastward along the front. The general
consensus of the most recent 12Z guidance indicates that widespread accumulations of 2-4 inches centered over parts of the Tennessee
and lower Ohio Valleys are likely (with locally higher amounts).
A large Slight Risk was once again maintained across the region,
reflecting the higher probabilities (50-70%) for 2 inches or more
shown by the GEFS/ECENS (and available CAMs) where this favorable
combination of deeper moisture, interacting with strong forcing,
along a relatively slow moving front, is expected to raise the
potential for heavy amounts late Saturday into early Sunday from
training storms. This remains a higher-end Slight Risk for parts of
the area, and a more focused corridor with the potential for an
upgrade to a Moderate Risk with the addition of more CAM data
extending fully into the period later today. The latest 00z
guidance indicates this potential remains highest from northeast Mississippi/northwest Alabama northeast through central Tennessee
into south-central Kentucky where locally higher totals of 5-6"
could be realized (as the FV3 in particular highlights). However,
have opted to remain at a higher-end Slight Risk for now as it is
difficult to pin down the targeted area that may need a Moderate
risk upgrade. The threat will be evaluated once again with the 12z
CAM suite with the potential for a targeted Moderate risk upgrade.

...Pacific Northwest...

Introduced a Marginal risk to portions of the Pacific Northwest
(mostly coastal/western Oregon and a bit of far northwestern CA)
with a notable uptick in QPF with this forecast cycle, suggesting
the potential for 2-5" localized rainfall totals along the coast
(with the highest amounts indicated in the OR/CA coastal border
area). This is due to a faster/stronger AR reaching into the Day 2
period (as an inherited Marginal risk has been maintained for this
update for Day 3) with IVT of 400-600 kg/ms indicated perpendicular
or nearly perpendicular to the coast from 21z Sat well into Day 3.

Churchill/Putnam/Pereira


Day 3
Valid 12Z Sun Mar 16 2025 - 12Z Mon Mar 17 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE EAST COAST, FROM THE SOUTHEAST TO NEW ENGLAND, AND FOR PORTIONS
OF THE PACIFIC NORTHWEST...

...East Coast...

As the aforementioned low lifts northward into Canada, what's left
is a weakening cold front as the upper-level pattern becomes a bit
less amplified (shortwave over the Southeast lifting a bit and
cutting off from northern/polar stream). The result looks to be
scattered localized totals of 1-2" over a large region from the
Southeast (central FL, southeast GA, and Carolinas) into the Mid-
Atlantic and portions of the Northeast/New England. The 00z GEFS
and ECENS both show areas with the potential for 2-3" totals, but
they are not in agreement on the regions (GEFS showing potential
for the Mid-Atlantic to Northeast, while ECENS has lower probs
overall and centered from the Mid-Atlantic to the Southeast).

...Pacific Northwest...

The aforementioned AR looks to bring in stronger moisture transport
into Day 3 with the potential for IVT in the 600-800 kg/ms range
near the OR/CA border region for a period. Model consensus suggests
an additional 2-4" QPF through Day 3, and that could necessitate a
targeted upgrade to Slight risk in future updates (depending on
forecast consistency and trends in the next cycle or two).

Churchill

$$
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FOUS30 KWBC 142026
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
426 PM EDT Fri Mar 14 2025

Day 1
Valid 16Z Fri Mar 14 2025 - 12Z Sat Mar 15 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE LOWER TO MID MISSISSIPPI VALLEY INTO PARTS OF THE OHIO AND
TENNESSEE VALLEYS...

A deepening mid-level upper low will move northeastward today from
the southern Plains and over the Middle Mississippi Valley. At the
same time, strengthening southerly flow will help to advect a
moist, unstable airmass increasingly northward and ahead of an
eastward moving cold front. Storms are expected to rapidly develop
along the cold front by late afternoon possibly as far west as the
Middle/Lower Missouri Valley before increasing in coverage as the
front reaches the Middle Mississippi Valley this evening, with
eventual development also extending southward into the Tennessee
Valley. Both the front and accompanying storm motions are expected
to remain rather quick moving given the strong dynamics in place.
Therefore, this convection will almost certainly pose more of a
severe risk than a flash flood threat. However, given the strong
dynamics, along with sufficient instability for deep convection,
expect peak rainfall rates will be briefly intense enough
(~1-2"/hr) to produce localized amounts that exceed current model
forecasts (2-3 inches over relatively short period) which could
lead to some isolated flash flooding particularly in urban areas.
There is also an increasing signal in the guidance that some
additional storms may develop ahead of the front as an 850 mb jet
ramps up from the Lower Mississippi Valley into the Tennessee
Valley in the evening/overnight hours. These storms would also pose
a threat for some locally heavy rain rates and the potential for a
quick 2-3 inches of rainfall.

Putnam


Day 2
Valid 12Z Sat Mar 15 2025 - 12Z Sun Mar 16 2025

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

...Ohio and Tennessee Valleys...

The upper-level pattern will remain amplified Saturday across the
central U.S. as one upper-low lifts northward into Canada while a
second upstream shortwave/upper jet dives southeast into the
southern Plains on Saturday morning and spreads eastward over the
Lower Mississippi Valley/Southeast into Saturday afternoon/evening.
A surface wave developing along the leading system's trailing cold
front will help focus deep Gulf moisture tapped by a very strong
850 mb jet while supported aloft by increasing upper-level
divergence ahead of the approach of the upper jet. This will help
lead to the continued development and maintenance of both open warm
sector convective development along the leading edge of the moist
warm air advection/850mb jet as well as along the slowing eastward
moving cold front. The updated 12Z CAM guidance supports the most
likely corridor of overlap between the warm sector development as
well as potential repeated/training rounds of storms along and just
ahead of the cold front across portions of the Tennessee Valley
from northeastern Mississippi east-northeastward into northern
Alabama, south-central/southeastern Tennessee, and northwestern
Georgia. This region also coincides with areal average QPF amongst
the CAM guidance of 3-6", with locally higher totals of 8"+, and
HREF probabilities of greater than 5" of rainfall over 50%. These
very heavy rainfall totals, supported by downpours of 2"+/hour,
will have the potential to lead to widespread, significant
instances of flash flooding, with an upgrade to a Moderate Risk now
included for the region. While there is greater uncertainty, the
latest 12Z guidance also shows support for similar totals further
northeastward into portions of south- central/southeastern Kentucky
as well as further eastward into western North Carolina, which may
require an expansion of the Moderate Risk if confidence increases.
Areas of south-central/southeastern Kentucky as well as western
North Carolina also remain more sensitive to additional rainfall.
Regardless, a broader area of average rainfall totals of 2-3",
locally higher, will contribute to additional scattered to
potentially numerous instances of flash flooding across the
Tennessee and Ohio Valleys within the Slight Risk.

...Pacific Northwest...

A Marginal Risk remains in place for portions of the Pacific
Northwest (mostly coastal/western Oregon and a bit of far
northwestern CA) where guidance continues to indicate the potential
for 2-5" localized rainfall totals along the coast (with the
highest amounts indicated in the OR/CA coastal border area). This
is due to a faster/stronger AR reaching into the Day 2 period from
Saturday evening into early Sunday morning (as an inherited
Marginal risk has been maintained for this update for Day 3) with
IVT of 400-600 kg/ms indicated perpendicular or nearly
perpendicular to the coast that will continue into Day 3. A
targeted upgrade to a Slight Risk may be necessary on Day 2 and/or
Day 3 as confidence increases in the timing of the heaviest
rainfall given it may very well split different portions of both
periods.

Putnam/Churchill


Day 3
Valid 12Z Sun Mar 16 2025 - 12Z Mon Mar 17 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE EAST COAST, FROM THE SOUTHEAST TO NEW ENGLAND, AND FOR PORTIONS
OF THE PACIFIC NORTHWEST...

...East Coast...

As the aforementioned low lifts northward into Canada, what's left
is a weakening cold front as the upper-level pattern becomes a bit
less amplified (shortwave over the Southeast lifting a bit and
cutting off from northern/polar stream). The result looks to be
scattered localized totals of 1-2" over a large region from the
Southeast (central FL, southeast GA, and Carolinas) into the Mid-
Atlantic and portions of the Northeast/New England. The 12z
GFS/ECMWF as well as GEFS and ECENS both show the potential for
locally higher totals of 2-3", with more confidence in these totals
being realized over portions of the eastern Carolinas, and then
less likely further north into the Mid-Atlantic/Northeast/New
England as well as further south into northern Florida. Regardless,
these totals look to remain somewhat limited as the front begins a
faster progression towards the Atlantic Coast.

...Pacific Northwest...

The aforementioned AR looks to bring in stronger moisture
transport into Day 3 with the potential for IVT in the 600-800
kg/ms range near the OR/CA border region, peaking for a period
early in the day on Sunday. Model consensus suggests an additional
2-4" of QPF through Day 3, and a targeted upgrade to Slight risk
remains possible in the day 3 period (as well as day 2) in future
updates depending on forecast consistency and greater confidence on
the exact timing of the window of heaviest rainfall, which may not
evenly split the day 2/3 period.

Putnam/Churchill

$$
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FOUS30 KWBC 150820
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
420 AM EDT Sat Mar 15 2025

Day 1
Valid 12Z Sat Mar 15 2025 - 12Z Sun Mar 16 2025

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE MID-SOUTH INTO THE TENNESSEE VALLEY...

...Ohio and Tennessee Valleys...

The upper-level pattern remains amplified today across the central
U.S. as one upper-low lifts northward into Canada while a second
upstream shortwave/upper jet dives southeast into the southern
Plains this morning and spreads eastward over the Lower Mississippi Valley/Southeast into the afternoon/evening. A surface wave
developing along the leading system's trailing cold front will help
focus deep Gulf moisture tapped by a very strong 850 mb jet while
supported aloft by increasing upper-level divergence ahead of the
approach of the upper jet. This will help lead to the continued
development and maintenance of both open warm sector convective
development along the leading edge of the moist warm air
advection/850mb jet as well as along the slowing eastward moving
cold front. The updated 00z CAM guidance supports the most likely
corridor of overlap between the warm sector development as well as
potential repeated/training rounds of storms along and just ahead
of the cold front across portions of the Tennessee Valley from
northeastern Mississippi east-northeastward into northern Alabama,
much of Tennessee into southern Kentucky, and northwestern Georgia
into far southwestern North Carolina. This region coincides with
HREF PMM QPF values of 3-6", with locally higher amounts (as well
as HREF 40-km neighborhood probabilities of 5" exceedance of
20-60%). Strong convection with an anticipated storm mode
supporting discrete supercells will allow for locally extreme
rainfall rates of 2"+/hr at times, leading to flash flooding over
more sensitive terrain without a consideration of training. But as
much of this discrete convection will occur out ahead of the main
line of storms, some training is also anticipated (which could lead
to the localized totals of 6"+).

The inherited Moderate risk area was expanded with this update,
mostly to the north and west to include more of Tennessee, and a
bit more of northern MS and edging into south-central Kentucky.
This generally encompasses the area where the HREF exceedance
probabilities suggest a heightened risk of 3-5"+ totals (40-km
neighborhood 3" exceedance probabilities of 50-100%, and 5" values
of 20-60%). The axis of highest probabilities exists from far
northwestern Mississippi into Middle Tennessee and far south-
central Kentucky (40-60% corridor for 5" exceedance), where this
could be considered a higher-end Moderate risk (as 6-hr FFGs are
2.5-3.0", and the vast majority of this rainfall will occur over
that short a period). As is typically the case with Moderate risk
events, there is an elevated risk of localized significant flash
flooding, particularly if extreme training/totals develop near
sensitive terrain and/or urban areas.

...Pacific Northwest...

A Marginal Risk remains in place for portions of the Pacific
Northwest (mostly coastal/western Oregon and a bit of far
northwestern CA) where guidance continues to indicate the
potential for 2-5" localized rainfall totals along the coast (with
the highest amounts indicated in the OR/CA coastal border area).
This is due to an the arrival of an AR this evening with forecast
IVT of 400-600 kg/ms indicated perpendicular (or nearly
perpendicular) to the coast (which will continue well into Day 2).

Churchill/Putnam


Day 2
Valid 12Z Sun Mar 16 2025 - 12Z Mon Mar 17 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE EAST COAST, FROM THE SOUTHEAST TO NEW ENGLAND, AND FOR PORTIONS
OF THE PACIFIC NORTHWEST...

...East Coast...

As the aforementioned low lifts northward into Canada, what's left
is a weakening cold front as the upper-level pattern becomes a bit
less amplified (shortwave over the Southeast lifting a bit and
cutting off from northern/polar stream). The result still looks to
be scattered localized totals of 1-2" over a large region from the
Southeast (central FL, southeast GA, and Carolinas) into the Mid-
Atlantic and portions of the Northeast/New England (though some
2-3" totals are possible in the coastal Carolinas region). The
Marginal risk was maintained as these relatively limited totals
should only present a localized flash flood risk as the front
begins a faster progression towards the Atlantic Coast.

...Pacific Northwest...

The aforementioned AR looks to bring in stronger moisture
transport into Day 2 period with the potential for IVT in the
600-800 kg/ms range near the OR/CA border region, peaking for a
period early in the day on Sunday. Model consensus suggests an
additional 2-4" of QPF through Day 2, and a targeted upgrade to
Slight risk remains possible (depending on the evolution of the
forecast QPF in the Day 1 period).

Churchill/Putnam


Day 3
Valid 12Z Mon Mar 17 2025 - 12Z Tue Mar 18 2025

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

Churchill
$$
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FOUS30 KWBC 220733
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
333 AM EDT Sat Mar 22 2025

Day 1
Valid 12Z Sat Mar 22 2025 - 12Z Sun Mar 23 2025

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

Wegman


Day 2
Valid 12Z Sun Mar 23 2025 - 12Z Mon Mar 24 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
WESTERN WASHINGTON STATE AS WELL AS FOR PORTIONS OF THE LOWER
MISSISSIPPI AND TENNESSEE VALLEYS...

...Western Washington State...

The trailing cold front of a low moving into British Columbia will
move into the Pacific coast of Washington State on Sunday. The
front will usher in a period of strong westerly fetch off the
Pacific. This will keep a steady supply of moist upslope flow into
the Olympics and Washington Cascades. 3 to 5 inches of rain are
expected into those ranges Sunday and Sunday night. The inherited
Marginal Risk was largely unchanged, with the greatest chances of
isolated flash flooding on the west facing slopes of those ranges.
The Skokomish River remains the river with the highest potential
for flooding given its low thresholds for flooding. Further, the
soils are already near saturation in this area given the multiple
rounds of rain the area has seen over the last several weeks, so
most of the rainfall expected should convert to runoff.

...Portions of the Lower Mississippi and Tennessee Valleys...

A slow-moving cold front will move southeastward across portions of
the Mid-South Sunday afternoon through Sunday night. The front will
be supported by an LLJ of Gulf moisture, which will be aligned
southwest to northeast, or parallel to the frontal interface. This
will support some training convection, despite only modest Gulf
moisture. The potential for some training over areas that got heavy
rain a few days ago could lead to isolated instances of flash
flooding, especially in low-lying flood-prone areas and urban
areas. FFGs are quite high across the Mississippi Valley but
decrease markedly across the Tennessee Valley due to recent heavy
rain. However, the further north you go, the less instability there
will be, which will effectively cap how strong the storms will be.
The front will have enough forward speed to also limit the
potential for training as well. Given all of these above factors,
there have been few changes to the ERO for this area.

Further northeast into West Virginia, the latest forecast rainfall
has come down significantly from previous forecasts. Due to a lack
of instability. the rainfall is not expected to remain heavy for
long as individual cells track northeastward along the front.
Despite very low FFGs, expect much of the rainfall in this area to
be stratiform, greatly limiting the flash flood potential, despite
some topography the rain will have to overcome to cause flooding.
With the broader forecast now under a half inch in much of northern
West Virginia, the inherited Marginal Risk in this area has been
downgraded.

Wegman


Day 3
Valid 12Z Mon Mar 24 2025 - 12Z Tue Mar 25 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR MUCH OF THE
CENTRAL GULF COAST...

The front that moved across the Lower Mississippi Valley on Sunday
will continue to the Gulf Coast on Monday before stalling. There
remains some potential for instability and modest moisture (by Gulf
Coast standards) to support heavy rainfall from training storms,
but the primary flash flooding threat will be in the urban areas
from New Orleans east through Pensacola and the Florida Panhandle.
The inherited Marginal Risk area was trimmed on the northern end
where high FFGs and a meager expected rainfall should preclude any
flash flooding concerns into interior southern Alabama and Georgia.

Wegman

$$
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FOUS30 KWBC 160825
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
425 AM EDT Sun Mar 16 2025

Day 1
Valid 12Z Sun Mar 16 2025 - 12Z Mon Mar 17 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE EAST COAST FROM SOUTH CAROLINA THROUGH SOUTHERN NEW ENGLAND,
AND FOR PORTIONS OF NORTHERN CALIFORNIA AND SOUTHWEST OREGON...

...East Coast...

A progressive cold front and negatively tilted longwave trough
will traverse much of the East Coast today, as the upper-level
pattern becomes a bit less amplified (shortwave over the Southeast
cutting off from northern/polar stream with ridging building over
central CONUS). Convection in association with the front looks to
generally result in areal average totals of 1.0-1.5" (per latest
WPC QPF), but the latest CAMs (00z HREF suite) suggests relatively
high odds (30-50%+) for localized totals in excessive of 2" (per
40-km neighborhood probabilities). The inherited Marginal risk area
was expanded a bit to generally encompass where 2" exceedance probs
are 30%+ (but excluding FL and much of southeast GA, as FFGs are
particularly high here). While this is a lower-end Marginal risk
for most places, the risk is maximized over coastal NC where 3"
exceedance probs are 40-60%.

...Southwest Oregon into Northern California...

A relatively weak and narrow atmospheric river (AR) will continue
to bring moderate to heavy rainfall to the OR/CA coastal border
region with additional forecast localized totals today of 2-5".
Most of this rainfall will be spread out over a 12-18 hour period
with peak rates staying under 1"/hr due to a lack of instability
(though 1"/hr rates may be reached for a brief period near the
CA/OR border along the coast where the HREF indicates MU CAPE up to
nearly 500 J/kg). Maintained the inherited Marginal risk, though a
future targeted upgrade to Slight risk remains possible (depending
on the evolution of rainfall this morning and any upticks in QPF in
the 12z HREF suite).

Churchill


Day 2
Valid 12Z Mon Mar 17 2025 - 12Z Tue Mar 18 2025

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

Churchill


Day 3
Valid 12Z Tue Mar 18 2025 - 12Z Wed Mar 19 2025

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

Churchill

$$
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FOUS30 KWBC 230800
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
400 AM EDT Sun Mar 23 2025

Day 1
Valid 12Z Sun Mar 23 2025 - 12Z Mon Mar 24 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
WESTERN WASHINGTON STATE...

...Western Washington...

In coordination with SEW/Seattle, WA forecast office, a Slight Risk
upgrade was introduced with this forecast update. A strong cold
front and trailing atmospheric river plume are moving into the
coast of Washington State now, and will continue to push west into
the Olympic Mountains and Cascades through the day today. As the
front moves into the mountains, the combination of forcings from
the front, the upslope flow, and abundant Pacific moisture both
with and behind the front will increase the potential for half-inch
per hour rainfall rates into the mountains. Meanwhile, an
increasingly southerly component of the onshore flow associated
with the following atmospheric river will advect warmer air into
the region. This will result in rising snow levels above 7,000 ft,
which will increase the potential for resultant flooding from
higher elevation snowmelt and the heavy rainfall.

IVT values associated with the trailing atmospheric river have
risen a bit in the latest guidance, peaking in the 625 to 675 kg/ms
range today. This increase along with slightly greater amounts of
atmospheric moisture have resulted in higher forecast rainfall
today, especially during the daylight hours as the front moves
ashore. The front being either primary or a significant component
of the forcing will result in the heaviest precipitation into the
Olympics and Cascades today. Once the front dissipates as it is
shredded by the mountains, the atmospheric river and upslope flow
will not have nearly the amount of forcing alone as they had with
the front. Thus, the potential for heavy rainfall rates above a
quarter inch per hour should diminish by tonight.

Soils in this area remain nearly saturated from repeated rounds of
rain across western Washington in recent weeks. Therefore most, if
not all the rainfall today should convert to runoff. Expect 4 to 6
inches of rain, with locally higher amounts west of the Olympics,
and 3-5 inches into the northern Cascades northeast of Seattle. For
the Seattle area, significantly less rain, on the order of a
fraction of an inch is expected, as rain shadowing off the Olympics
will greatly cut into rainfall totals. This will be partially
offset by the urbanization in the area, so the Marginal Risk
remains largely unchanged. The Slight Risk upgrade is focused on
the wettest areas, namely west of the Olympics and the western
foothills of the northern Cascades into Whatcom and Skagit Counties.

...Lower Mississippi and Tennessee Valleys...

Very few changes were needed with this update across the Lower
Mississippi and Tennessee Valleys. A progressive cold front moving
across the middle of the country will continue south and east into
the Southeast today. This evening through tonight, the front will
run into a strengthening low-level jet (LLJ), which will align
along the frontal interface as it moves into the Mid-South.
Scattered showers and thunderstorms will develop ahead of the front
as a result, which in a few instances may train over the same
areas, but modest Gulf moisture and instability to 2,000 J/kg
should limit storm strength, notwithstanding their fast motion. The
inherited Marginal Risk is largely unchanged, stretching northeast
from northern Louisiana to the southern Appalachians. Soils have
largely dried since the last heavy rain event in this area, so any
flash flooding will be isolated to typical flood prone and urban areas.

Wegman


Day 2
Valid 12Z Mon Mar 24 2025 - 12Z Tue Mar 25 2025

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

In coordination with MOB/Mobile, AL and TAE/Tallahassee, FL
forecast offices, the inherited Marginal Risk for portions of the
central Gulf Coast was downgraded with this update. The front
moving across the Southeast will continue across the Gulf Coast
Monday morning, and is now largely expected to continue into the
northern Gulf, as well as towards the Georgia coast during the day.
Any storms from the overnight period Monday morning will continue
eastward and remain progressive enough that training is unlikely.
There will remain some Gulf moisture and instability, but these too
will be modest, and generally unsupportive of the heavy rainfall
rates needed to overcome the high FFGs along the Gulf Coast. With
areal rainfall now generally under a half inch, and in many areas
under a quarter inch (outside of any heavier rain cores), and the
expected continued movement of the front and associated storms, the
flash flooding potential has continued the trend of decreasing from
previous days. For these reasons, the Marginal was dropped.

Wegman


Day 3
Valid 12Z Tue Mar 25 2025 - 12Z Wed Mar 26 2025

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

Very late Tuesday night (generally from around 06Z Wed on), the
collision of return flow off the Gulf in the form of 15-25 kt SSW
flow over Texas will run into a slow-moving warm front along the
Red River. Model guidance has hinted for a few days now that an
area of storms, possibly a small MCS, will develop over either
southeast Oklahoma or northeast Texas along this front. While there
has been model consistency, the area of storms remains small, and
somewhat uncertain as to where it will set up. This area of the
country has been very dry of late, which too precludes much
flooding. Given the small area that would be impacted, the area
remains without a Risk area for now, but will continue to be
monitored for possible introduction of a Marginal with CAMs
guidance or improved agreement on a wetter forecast.

Wegman

$$
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FOUS30 KWBC 240740
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
340 AM EDT Mon Mar 24 2025

Day 1
Valid 12Z Mon Mar 24 2025 - 12Z Tue Mar 25 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
NORTHWEST WASHINGTON STATE...

...Olympic Peninsula and Northern Cascades in Northwest
Washington... A Marginal Risk of excessive rainfall will continue
during Day 1 over the Olympic Ranges and across the foothills and
western slopes of the northern Cascades, as the modest Atmospheric
River slowly diminishes today and Monday night. Given continuation
of the AR event, this too is a continuation of the previous
(yesterday's) ERO, albeit with a drop in the category across the
board. In other words, a Marginal Risk is in effect across areas
where there was a Slight in yesterday's D1 ERO, while areas in
yesterday's Marginal are now within the <5% probability of
exceeding flash flood guidance.

Latest guidance shows an atmospheric river continuing to impact
the region, but also gradually waning through the period. The 00Z
GEFS shows IVTs decreasing from ~500 kg/m/sec early in the period
to 300-350 kg/m/sec, as a ridge continues to build and onshore
flow into the region diminishes. As the AR diminishes, so will the
potential for additional heavy precipitation. However, the continued
moisture flux into the region early in the period may be sufficient
for additional amounts of 2-3 inches, as indicated by the 00Z
HREF. These amounts along with additional snowmelt may prolong
runoff concerns.

Hurley


Day 2
Valid 12Z Tue Mar 25 2025 - 12Z Wed Mar 26 2025

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

Hurley


Day 3
Valid 12Z Wed Mar 26 2025 - 12Z Thu Mar 27 2025

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

Hurley

$$
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FOUS30 KWBC 250822
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
422 AM EDT Tue Mar 25 2025

Day 1
Valid 12Z Tue Mar 25 2025 - 12Z Wed Mar 26 2025

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

Hurley


Day 2
Valid 12Z Wed Mar 26 2025 - 12Z Thu Mar 27 2025

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

Diffuse mid-upper level trough moving slowly eastward across the
Southwest-Four Corners Region will lead to an uptick in upper
diffluence across northern Mexico and SC-South TX Wed and Wed
night, with a WNW-ESE lobe of mid level vorticity (shear axis)
lifting northeast across the outlook area along the elevated warm
between 18Z Wed and 12Z Thu. Strengthening low-level inflow (30-40
kts at 850 mb) will boost the low-level moisture transport, with
TPW values climbing between 1.75-2.00".

Convection initiating across the Sierra Madre in northeast Mexico
will cross into SC and South TX Wed afternoon and overnight, and
while considerable shear in the low-mid levels should keep the
convection moving along, the slow progression of the mid-upper
trough will likely result in slow-moving and/or repetitive areas
of more organized convection, as evidenced by the higher-end QPF
totals per the latest (00Z Tue) guidance...as much as 5-7+ inches
per the Regional GEM, ECMWF, and FV3. Dry antecedent soils and
initially high FFG values (3-4" over a large portion of the outlook
area) will likely result in a more limited or localized flash
flood threat, and as a result, have hoisted a Marginal Risk across
these areas in the Day 2 ERO.

Hurley


Day 3
Valid 12Z Thu Mar 27 2025 - 12Z Fri Mar 28 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF SOUTH-CENTRAL AND SOUTH TEXAS AND MUCH OF THE TEXAS GULF COAST...

...Southern Texas...
Aforementioned southern stream trough pivots slowly eastward across
the Southern Plains Thu-Thu night. Rather healthy, deep-layer exit
region forcing continues, with low-mid level moisture flux
anomalies increasing to near 3 standard deviations above normal
(TPW anomalies per the 00Z 3/25 GEFS) while 1.75-2.00" TPW values
overspread the outlook areas. Continued healthy low-level inflow
off the Gulf, becoming more parallel to the mean 850-300 mb flow
with time by late Thursday, will lead to an increase in upward
propagation and thus potential for cell training Thursday evening
and overnight. This as low-level inflow taps the more unstable
airmass (1000-1500 J/Kg mixed-layer CAPEs) across the western Gulf.

The guidance is beginning to converge with the heavy rainfall
signal with the 00Z 3/25 models, as the GFS, ECMWF, GEM (esp. GEM
Regional), and UKMet now all show a corridor of 4-8+ inches of
rain across portions of SC-South TX into the Gulf Coast during the
24hr period from 12Z Thu-12Z Fri. While there is still some areal
and timing differences, the growing model consistency (especially
among these global runs) has bolstered the confidence for a more
targeted Slight Risk area, including areas closer to the Coast
that for now would likely end up being a higher-end Slight Risk
despite the dry antecedent soils.

These areas (closer to the Gulf coast) would also be an area to
watch for a potential upgrade to Moderate Risk during subsequent
outlooks, given the closer proximity to the more unstable airmass
just off the coast and thus the greater potential for multiple
hours of 2.0+ in/hr rainfall rates (higher probability of >6" of
total rainfall), especially late Thu-Thu night with any cell training.

...Pacific Northwest...
Another modest Atmospheric River (narrow ribbon of 500+ kg/m/s
IVTs) will result in pockets of 3-5+ inch 24 hour rainfall totals
along the West Coast from Northern CA northward through OR-WA.
Among the 00Z 3/25 models, the Regional GEM is by far the wettest,
with isolated totals of 6-8+ inches. Despite the lack of
instability, the wet antecedent soils along with the potential of
0.3-0.5 in/hr rainfall rates could lead to localized short-term
runoff issues, particularly along small streams and over burn
scars.

Hurley


$$
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FOUS30 KWBC 260819
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
419 AM EDT Wed Mar 26 2025

Day 1
Valid 12Z Wed Mar 26 2025 - 12Z Thu Mar 27 2025

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF SOUTH-CENTRAL AND SOUTH TEXAS...

Model guidance continues to become better clustered in terms of the
timing and areal extent of a heavy rainfall signal across SC-South
TX later this afternoon and overnight. Increasing upper level
difluence and DPVA ahead of a slow moving upper trough will
initiate organized convection across along the Rio Grande in SW TX
later this afternoon, which will begin to grow upscale toward the
evening hours given the uptick in SSE low-level inflow (25-40+ kts
at 850 mb). This area has been very dry and could use the rain,
unfortunately this setup looks good enough to be a case where it's
beneficial rain initially, but then quickly overwhelms even the dry
soil conditions. Model soundings by Wed afternoon/evening show a
deeply saturated profile with good directional shear and moderate
instability. This should support some convective clusters with some
weak mesocyclones and right mover motions are very slow. Combine
that with the front nearby and anticipate upscale growth of slow
moving convective clusters through Wed night within an environment
capable of 2-3" per hour rainfall. Activity may eventually grow
upscale enough that it begins propagating east and possibly
offshore, however even if that eventually transpires, there will
still be a prolonged period where training convection is a possibility.

Overall there is above average model agreement on this overall
evolution. Moreover, the latest (00Z) HREF probabilities have
bumped up over the past few runs, including probabilities >50% of
greater than 5" of rain in 24hrs (which is a good proxy for a
Moderate Risk area based on verification). There is also a chance
for an upgrade to High Risk within the Moderate Risk area, albeit
quite narrow. This is where the HREF has 70+ probs of rainfall
exceeding 5"/24hrs, along with 40-50% probs of >8"/24hrs.

While confidence on the event happening is above average, there is
still uncertainty on the exact axis of heaviest rainfall, which
will probably be somewhat narrow in nature. The 00Z ECMWF in fact
came down considerably with the QPF during day 1, and as with its
previous run, again has more of a diffuse look with multiple axes
of heavier rain on either side of the Moderate Risk area. So again,
the MDT risk is centered around the highest HREF probabilities,
and generally on the southern gradient of the global model QPF
solutions. In fact, changes made to the previous (Day 2) ERO
include pulling the southern boundaries of the Moderate, Slight,
and Marginal Risk areas a bit farther south across South TX. Flash
flood coverage over this area is expected to increase Wednesday
night into Thursday morning, and locally significant impacts are possible.

...Pacific Northwest...
A Marginal risk continues across portions of western OR and WA.
Convection is expected to develop over portions of southwest OR by
21z Wed and then track off to the north through the afternoon and
evening hours. An anomalous amounts of CAPE is forecast,
potentially upwards of 2000 j/kg, and PWs are forecast over the
climatological 90th percentile. This combination of CAPE and PWs
supports intense rainfall rates. These cells should be quick moving
and the bigger hazard is probably severe weather (as highlighted
by the SPC Slight risk), however the intense rainfall rates
producing over 1" in an hour may be enough for localized flash
flood concerns. Areas of terrain, urban areas, and low lying areas
will be most prone to localized flash flooding driven by these
short duration intense rainfall rates.

Hurley/Chenard


Day 2
Valid 12Z Thu Mar 27 2025 - 12Z Fri Mar 28 2025

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF SOUTH-CENTRAL AND SOUTH TEXAS AND MUCH OF THE TEXAS GULF COAST...

...South Texas...
Minimal changes were made to the Day 2 ERO areas inherited from
yesterday's Day 3 outlook. Based on the latest guidance trends, we
did nudge the Moderate Risk a bit farther up the Middle TX Coast.

The event described in the day 1 discussion over south TX will
continue into Thursday. There is a bit more uncertainty on the
details by this time as convective evolution will likely be
impacted by mesoscale influences of the day 1 convection. On the
synoptic scale, ingredients are likely even more favorable for
heavy rainfall on day 3 then they were on day 2. Large scale
forcing should reload and be even a bit stronger as the mid level
trough axis and associated shortwave energy moves across the area
(enhancing the upper divergence/DPVA).

However, the extent of the excessive rainfall risk will likely be
at least partially dependent on mesoscale factors...such as the
outflow location form the day 1 convection and its impact on
instability. The expectation is that the outflow boundary will be
near the coast by this time, and so that is where the greatest
focus for training convection is expected on Thursday, and thus
where the MDT risk is in place. There is some chance this is
offshore by 12z Thursday, but the current consensus suggests it may
struggle to clear the coast, leaving coastal areas susceptible to
additional heavy rainfall and flash flooding. Even if instability
is eroded by Thursday, the increase in forcing and southerly flow
should be enough to destabilize portions of the area again with
time, and so do think at least some flash flood risk exists even in
a scenario where convection initially propagates offshore,
especially Thu night with the uptick in S-SSE low-level flow.

Overall confidence is high in a flash flood event, but confidence
in the details by Thursday-Thu night remains low. In a worst case
scenario outflow stalls near the coast allowing for repeat
convection and a significant flash flood event could evolve. In a
best case scenario convection propagates offshore, but
redevelopment later in the day still results in some flash flood
threat, albeit probably less significant. When combining day 2 and
3 it seems probable that some areas receive 5-10" of rain over
south TX, and localized amounts of 10-15" are certainly possible.
Confidence is increasing in the coverage of flash flooding and the
possibility of at least localized significant impacts, warranting
the Moderate risks on both days 2 and 3.

...MS and OH Valley...
A Marginal risk continues from yesterday's Day 3 ERO across portions
of northern MO, southern IA, IL and central/southern IN. A
stationary front draped across this region will gradually lift
north as a warm front through the period. Southerly flow will
result in an uptick in instability and moisture, and at least
scattered convection is expected Thursday into Thursday night.
There is at least some chance for organized convective development
near the front, which could briefly train from west to east. Global
model QPF is locally as high as 1-3" along this corridor, and
given the expected convective nature of activity, this would
suggest isolated amounts over 3" are probable. A localized, and
generally minor, flash flood risk could result.

...Pacific Northwest...
Another modest Atmospheric River (narrow ribbon of 500+ kg/m/s
IVTs) will result in pockets of 3-5+ inch 24 hour rainfall totals
along the West Coast from Northern CA northward through OR-WA.
Among the 00Z 3/25 models, the Regional GEM is by far the wettest,
with isolated totals of 6-8+ inches. Despite the lack of
instability, the wet antecedent soils along with the potential of
0.3-0.5 in/hr rainfall rates could lead to localized short-term
runoff issues, particularly along small streams and over burn scars.

Chenard/Hurley


Day 3
Valid 12Z Fri Mar 28 2025 - 12Z Sat Mar 29 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE UPPER TEXAS COAST THROUGH SOUTHWEST AND SOUTH-CENTRAL LOUISIANA...

Slow-moving mid-upper trough will push the area of most favorable
deep-layer forcing (upper divergence/diffluence and DPVA) farther
east along the Gulf Coast. Coincident with the favorable synoptic-scale forcing, TPWs between 1.75-2.00", along with mixed layer CAPEs
around 1000-1500 J/Kg, will result in a more enhanced excessive
rainfall threat (i.e. Slight) across the Upper TX Coast to
Southwest and South-Central LA. Attributing to a lower risk
(Slight) compared to the previous days (Moderate) will be the
weakening low-level flow, which given the more limited deep-layer
shear, would more likely result in more effective convective outflows
and thus shorter duration of the more intense updrafts and heavier
rainfall cores.

Hurley

$$
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FOUS30 KWBC 270827
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
427 AM EDT Thu Mar 27 2025

Day 1
Valid 12Z Thu Mar 27 2025 - 12Z Fri Mar 28 2025

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF SOUTH-CENTRAL TEXAS AND THE MIDDLE/LOWER TEXAS GULF COAST...

...South Texas...
Periods of heavy rainfall over South TX will continue into today
and tonight, as ample moisture, shear, and instability (which will
reload today via both daytime heating and decreasing lapse rates
aloft) remain in place. That said, spatially uncertainty remains
relatively high for a Day 1 outlook, as mesoscale factors this
morning may have a large impact on the ultimate evolution of
convection (best expressed by the lack of consistency from hourly
runs of the HRRR, as well as the 00z HRRR being an outlier from
most of the other CAMs with regard to QPF maxima). On the synoptic
scale, ingredients are more favorable for heavy rainfall than
yesterday, and large scale forcing should reload with the mid-
level trough axis and associated shortwave energy moving across
the area (enhancing the upper divergence/DPVA).

However, the extent of the excessive rainfall risk will be at
least partially dependent on mesoscale factors, and observational
trends have already diverged somewhat significantly from the 00z
HREF consensus (with convection propagating farther south than
indicated, to near Brownsville). Despite these trends, the
inherited Moderate risk remains largely unchanged, as localized
3-5" totals over the past 12-24 hours have occurred within the
inherited area where additional training is expected. In fact, the
one area of expansion of the Moderate risk was to bring the contour
farther inland where FFGs have been depressed. While there is still
some chance that the bulk of convection is offshore by 12z,
observational and model trends suggests it may struggle to clear
the coast, leaving coastal areas susceptible to additional heavy
rainfall and flash flooding.

While a break in convective activity is somewhat likely by late
morning to midday, there is high confidence that scattered to
numerous instances of flash flooding will become likely again by
this afternoon and evening. In a worst case scenario, the outflow
stalls near the coast allowing for repeat convection and a
significant flash flood event could evolve (though an increase in
CAMs suggesting that the convection propagates fully offshore has
reduced this risk a bit). When combining rainfall that has already
occurred with what is forecast, it seems probable that some areas
receive 5-8" of storm totals, and localized amounts of 8-12" are
certainly possible.

...MS and OH Valley...
A Marginal risk was maintained (and shifted a bit west with
observational and model trends) across portions of northern MO,
southern IA, IL and central/southern IN. Warm-air advection and
overrunning near a stationary front draped across this region will
gradually lift north as a warm front through the period. In the
meantime, a short period of training this morning may result in
short-term 1-3" totals (per HREF PMM). A localized, and generally
minor, flash flood risk could result.

...Pacific Northwest...
Another modest Atmospheric River (narrow ribbon of 500+ kg/m/s
IVTs) will result in pockets of 3-5+ inch 24 hour rainfall totals
along the West Coast from Northern CA northward through OR-WA.
Despite the relative lack of instability, the wet antecedent soils
(along with the potential of 0.3-0.5 in/hr rainfall rates) could
lead to localized short-term runoff issues, particularly along
small streams and over burn scars.

Churchill/Chenard/Hurley


Day 2
Valid 12Z Fri Mar 28 2025 - 12Z Sat Mar 29 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE UPPER TEXAS COAST THROUGH SOUTHWEST AND SOUTH-CENTRAL LOUISIANA...

An inherited Slight risk area was maintained (and shifted a bit
west based on model trends) as a slow-moving mid-upper trough will
push the area of most favorable deep-layer forcing (upper divergence
and DPVA) farther east along the Gulf Coast. Coincident with the
favorable synoptic-scale forcing, TPWs between 1.75-2.00", along
with mixed layer CAPE around 1000-1500 J/Kg, will result in a more
enhanced excessive rainfall threat (i.e. Slight) across the Upper
TX Coast to Southwest and South-Central LA. Attributing to a lower
risk (Slight) compared to the previous days (Moderate) will be the
weakening low-level flow, which given the more limited deep-layer
shear, would more likely result in more effective convective
outflows and thus shorter duration of the more intense updrafts and
heavier rainfall cores (as well as generally drier antecedent
conditions). Considerable uncertainty still exists, as convective
details remain unclear at this point even on Day 1, but confidence
in 2-4" localized totals is increasing per the latest guidance.

Churchill/Hurley


Day 3
Valid 12Z Sat Mar 29 2025 - 12Z Sun Mar 30 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE CENTRAL GULF COAST...

A continuation of the decreasing flash flood risk is expected from
Day 2 into Day 3, as guidance largely indicates localized totals
of only 1-3" (mostly concentrated near the Central Gulf Coast
where FFGs are rather high). The inherited Marginal risk area was
trimmed rather significantly to the north (into the Mid-South), as
forcing and instability look rather minimal (with the ECMWF being
the wettest global model only indicating localized totals of 1-2").
A localized flash flood threat should result for areas confined
closer to the Gulf Coast (and mostly limited to more sensitive
urban areas).


Churchill

$$
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FOUS30 KWBC 210737
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
337 AM EDT Fri Mar 21 2025

Day 1
Valid 12Z Fri Mar 21 2025 - 12Z Sat Mar 22 2025

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

Wegman


Day 2
Valid 12Z Sat Mar 22 2025 - 12Z Sun Mar 23 2025

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

Wegman


Day 3
Valid 12Z Sun Mar 23 2025 - 12Z Mon Mar 24 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE LOWER MISSISSIPPI AND TENNESSEE VALLEYS AS WELL AS FOR THE
WESTERN OLYMPIC PENINSULA OF WASHINGTON STATE...

...Lower Mississippi and Tennessee Valleys...

A strong cold front trailing behind a deep low tracking across the
Upper Midwest will be the primary forcing supporting widespread
shower and thunderstorm activity across portions of the Mississippi
and Tennessee Valleys on Sunday. The front will be driven with a
robust longwave trough moving across the Midwest. Much of the
Marginal Risk area will be in the favorable RER of the jet. As is
typical with thunderstorm outbreaks, there will be an LLJ out of
the Gulf that will be in place ahead of the front. The
southwesterly LLJ will be parallel to the orientation of the front
(southwest to northeast), which will support training of the
leading convection. 5-10 kt southwesterly Corfidi Vectors further
support the potential for training. Thus, the forward speed of the
front, which should be slowing...but should be fast enough to limit
training potential...will be the deciding factor as to how
widespread the instances of flash flooding will be.

FFGs decrease markedly towards the north into the Ohio Valley, but
the lack of atmospheric instability in that region will keep most
of the rainfall in this area to stratiform rain. Further, when the
front is moving southeastward across the Ohio Valley, the forcing
and moisture availability will not be as optimized as a bit later
when the front is further south. Thus, the inherited Marginal Risk
over much of Kentucky and southern Indiana was trimmed with this
update. The greater instability and Gulf moisture will be closer to
the Gulf, where the Marginal Risk remains with this update. The
flooding threat will be partially offset by the higher FFGs in the
lower Mississippi Valley, so between that and the forward speed of
the front, instances of flash flooding should remain isolated,
favoring a continuation of the Marginal Risk. As always, a slowing
of the front or additional moisture/instability with future updates
could require a Slight Risk upgrade. Should the front become more
progressive then it's possible the Marginal Risk could be
downgraded or shrunk further.

...Olympic Peninsula of Washington...

A strong trailing cold front will move into the coast of the
Pacific Northwest on Sunday. IVT values will peak around 600-650
kg/ms during this time. The western Olympic Peninsula's soils are
well saturated from repeated rounds of rain over the past few
weeks, so this round could result in isolated flash flooding on the
smaller streams and creeks that drain the Olympic Mountains. There
were no changes to the inherited Marginal Risk. Expect 2 to 4
inches of new rainfall in the area through the day on Sunday.

Wegman

$$
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FOUS30 KWBC 280815
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
415 AM EDT Fri Mar 28 2025

Day 1
Valid 12Z Fri Mar 28 2025 - 12Z Sat Mar 29 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE UPPER TEXAS COAST THROUGH SOUTHWEST LOUISIANA...

An inherited Slight risk area was maintained (and adjusted) once
again for this update, as a slow-moving mid-upper trough will push
the area of most favorable deep-layer forcing (upper divergence and
DPVA) farther east along the Gulf Coast. However, considerably
uncertainty remains (especially for an initial Day 1 outlook) as
much is dependent on the evolution of convection this morning, as
convection continues to consolidate farther south than virtually
all of the guidance indicated at this time yesterday (resulting in
the heaviest rainfall totals of 6"+ over the past 24-48 hours
occurring over far South TX). Should a similar error occur today,
a Slight risk may well not verify (as the consolidating MCS at the
time of writing over far South TX will propagate offshore and may
prevent critically necessary moisture flux transport northward into
the Gulf coast, as best depicted by the 00z HRRR). In addition,
attributing to a lower risk (Slight) compared to the previous days
(Moderate) will be the weakening low-level flow, which given the
more limited deep-layer shear, would more likely result in more
effective convective outflows and thus shorter duration of the more
intense updrafts and heavier rainfall cores (as well as generally
drier antecedent conditions).

However, should more intense convection initiate and sustain
itself farther north (as much of the rest of the 00z HREF
indicates), then localized totals of 3-6"+ totals will be possible
from Southeast TX and the Upper TX coast through much of
southeastern LA (per 00z HREF PMM QPF and associated 40-km
neighborhood probabilities for 3" and 5" exceedance of ~30-60% and
~20-40%, respectively). Meteorological factors supporting this
potential include favorable synoptic-scale forcing (particularly
the continued impressive divergence aloft), precipitable water
values between 1.75-2.00", and CAPE building to 1000-1500 J/kg.
These same factors may still fuel intense convection offshore which
ultimately fail to materialize further inland, thus the Slight
risk is considered to be conditional. On that note, the Marginal
risk was also expanded southwestward to include South TX, given the
ongoing flooding and low-end potential for convective
redevelopment once again with daytime heating (though this
convection should be much less intense with the bulk of the forcing
shifting eastward).

Churchill


Day 2
Valid 12Z Sat Mar 29 2025 - 12Z Sun Mar 30 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE CENTRAL GULF COAST...

A continuation of the decreasing flash flood risk is expected from
Day 1 into Day 2, as ensemble guidance indicates the potential for
localized totals of 1-3" (mostly concentrated near the Gulf Coast
where FFGs are rather high). The limited inherited Marginal risk
area was maintained for this update, as forcing and instability
continue to look rather minimal (and most deterministic guidance at
this point indicates localized totals of less than 1" for the most
part, including the new WPC forecast, but decided to maintain the
Marginal for at least one more cycle to allow for new CAM data).
Any localized flash flood threat should mostly be confined closer
to the Gulf Coast (and limited to more sensitive urban areas).

Churchill


Day 3
Valid 12Z Sun Mar 30 2025 - 12Z Mon Mar 31 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE MISSISSIPPI, TENNESSEE, AND OHIO VALLEYS...

A much broader inherited Marginal risk area (relative to Day 2) has
been largely maintained (and expanded a bit), as multiple shortwave
troughs emerging from the Intermountain West and phase with the
polar jet and an associated longwave trough. This complex
interaction is expected to result in a broad area of convection
across much of the eastern CONUS, including portions of the MS, TN,
and OH Valleys. Despite the complexity of the synoptic and
mesoscale details, global models are in fairly good agreement in
indicating a convection breaking out across a broad warm sector
(characterized by PWATs of 1.5-2.0", SB CAPE of 1000-2000 J/kg, and
effective bulk shear of 40-60 kts). Most deterministic solutions
depict 1-3" localized totals (with 2-3" amounts most commonly
located farther south across the Lower MS Valley and Mid-South,
where better instability and moisture tend to be located) with both
the GEFS and ECENS indicating 2" exceedance potential (with the
GEFS favoring portions of the Mid-South from north MS into West and
Middle TN, while the ECENS favors locations farther southwest into
the MS Delta). These types of probabilities from the ensemble
guidance suggest that CAMs may well depict 2-4" localized totals,
and a targeted Slight risk introduction may be necessary in
subsequent outlooks (once better ensemble agreement and/or a
strengthening trend is more evident in the global guidance).

Churchill

$$
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FOUS30 KWBC 290800
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
400 AM EDT Sat Mar 29 2025

Day 1
Valid 12Z Sat Mar 29 2025 - 12Z Sun Mar 30 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE CENTRAL GULF COAST...

A lingering shortwave trough over the central Gulf Coast will
support a continuation of the decreasing flash flood risk (relative
to the past couple of days), as WPC QPF calls for areal average
totals on the order of 1-3" (concentrated in the vicinity of
coastal MS and adjacent portions of southeast LA). The 00z HREF
indicates surprisingly high odds of 5" exceedance (as high as
20-40% per a 40-km neighborhood method), especially considering
the overall decreasing trend in the forecast over the past couple
of days. Much of this is attributable to convective feedback from
the FV3 (large area of 9"+ totals, and not an uncommon phenomenon
from this particular CAM), but both the ARW and ARW2 also indicate
4-6"+ totals (though both of these models have been less than
stellar with the convection associated with this trough over the
past couple of days). Meanwhile, the 00z HRRR (as well as the NAM-
nest, for what it's worth) depicts much less significant totals
over land, indicating that some of the highest totals stay just
offshore (as well as a secondary maxima well north into central MS
with 2-4" localized totals). All this is to say, spatial
uncertainty remains higher than usual (as depicted by relatively
low probabilities of 2" exceedance, 10-20%, via 10-100 km Ensemble
Agreement Scale neighborhood probabilities). Given 3-6 hr FFGs
mostly in the 4-5" range along the coast (where the most intense
convection is most likely to occur, if it doesn't stay offshore
altogether), the limited inherited Marginal risk area was
maintained for this update (owing to the CAM model trends described
above, with forcing and instability continuing to look fairly
lackluster). Any localized flash flood threat should mostly be
confined closer to the Gulf Coast (and mostly limited to more
sensitive urban areas, which could be locally significant if
impacted by 5"+ totals).

Churchill


Day 2
Valid 12Z Sun Mar 30 2025 - 12Z Mon Mar 31 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE MISSISSIPPI, TENNESSEE, AND OHIO VALLEYS...

A much broader inherited Marginal risk area (relative to Day 1)
has been largely maintained, as a pair of shortwave troughs
emerge from the Intermountain West into the Central U.S. on
Sunday, eventually partially phasing with the polar jet (and an
associated longwave trough) by Sunday night. This complex
interaction is expected to result in a broad area of convection
across much of the eastern half of the CONUS, including portions of
the MS, TN, and OH Valleys. Despite the complexity of the synoptic
and mesoscale details, models remain in fairly good agreement in
indicating convection breaking out across a broad warm sector
(characterized by PWATs of 1.5-2.0", SB CAPE of 1000-2000 J/kg, and
effective bulk shear of 40-60 kts) supportive of discrete and
multi-cell clusters initially, and likely transitioning to more a
more linear QLCS orientation along the front into the evening (as
best depicted by the 00z FV3 and NAM-nest, which are the only CAMs
which extend through the full period at 00z). While WPC areal
average QPF calls generally for only 1-2" totals, most
deterministic solutions from the global models are likely well
underdone on localized totals, as CAMs will be needed to better
model the discrete convective initiation that is anticipated prior
to the main QLCS passage (with the FV3, NAM- nest, and CMC-reg all
indicating the potential for 3-5" totals, with probabilities
likely maximized in the vicinity of the Mid-South and MS Delta
regions where instability and moisture are more ideal... and this
is where a targeted Slight Risk is most likely to be introduced in
future updates, possibly as early as later today).

Churchill


Day 3
Valid 12Z Mon Mar 31 2025 - 12Z Tue Apr 01 2025

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

The aforementioned pair of shortwave troughs are progged to fully
separate by Day 3, as the northern stream shortwave continues to
phase with the polar jet (and associated parent longwave trough)
into the Mid-Atlantic/Northeast, while the southern shortwave
likely hangs back into the Mid-South and Lower MS Valley. This is
anticipated to result in a weaker setup overall for excessive
rainfall on Monday into Monday night, as the best dynamics and
upper-level forcing over the Northeast and Mid-Atlantic is
displaced from the best moisture and instability over portions of
the Southeast (where forcing from the secondary shortwave should
still be sufficient for organized convective activity). The
inherited Marginal risk was maintained for this portion of the
Southeast (including much of AL/GA with surrounding portions of
TN/NC/SC and MS), where GEFS/ECENS exceedance probabilities suggest
the best potential for 2-4" localized totals. Farther northeast
into the Mid-Atlantic and southern portions of New England, while
total tropospheric moisture will certainly be lower (~1.25" versus
1.5"+), these values are either equally or more anomalous than in
the Southeast (90th percentile or higher). Despite this, have
decided not to introduce a Marginal risk at this time, due to the
combination of marginal instability and progressive storm motions.

Churchill

$$
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FOUS30 KWBC 300815
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
415 AM EDT Sun Mar 30 2025

Day 1
Valid 12Z Sun Mar 30 2025 - 12Z Mon Mar 31 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE LOWER MISSISSIPPI, TENNESSEE, AND OHIO VALLEYS...

...Central Gulf Coast through the Ohio Valley...

A pair of shortwave troughs emerge from the Intermountain West
into the Central U.S. today, eventually partially phasing with the
polar jet (and an associated longwave trough) by later tonight.
This complex interaction is expected to result in a broad area of
organized convective activity across much of the eastern half of
the CONUS, including portions of the MS, TN, and OH Valleys.

Despite the continued complexity of the synoptic and mesoscale
details, models remain in fairly good agreement in indicating
convection breaking out across the broad warm sector today,
initially mostly discrete (and supportive of splitting supercells
and multicell clusters) and evolving into a QLCS ahead of the
associated cold front by this evening. Broad inflow from the Gulf
will result in precipitable water values of 1.25-1.75" (at or above
the 90th percentile, per CFSR climatology) and SB CAPE of 2000-4000
J/kg, as deep layer (0-6 km) shear increases to 40-60 kts. Hourly
rainfall rates of up to 2-3"/hr are possible in this environment,
initially highly localized in association with established
supercells, then more numerous to widespread with the passage of
the QLCS. Localized totals of 2-4" are generally expected within
the Slight for the whole of the event (with the majority falling in
a 3-6 hour period in association with the QLCS passage), with
totals near the upper-end of the range (~4") being possible where
storms train and/or where two or more mesocyclones align.

...Florida Peninsula/Southeasternmost Georgia...

A frontal boundary at 850 hPa slowly lifts through the state,
bringing precipitable water values to 1.5-1.75". MU CAPE maximizes
above 2000+ J/kg in South Florida. There appears to be enough
effective bulk shear for thunderstorm organization as well. The
model guidance --- mostly mesoscale -- indicates the potential for
local amounts in the 5" range. The Marginal risk was maintained.

Churchill/Roth


Day 2
Valid 12Z Mon Mar 31 2025 - 12Z Tue Apr 01 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE SOUTHEAST & NORTHEAST...

...Southeast...

The aforementioned pair of shortwave troughs are progged to fully
separate by Day 2, as the northern stream shortwave continues to
phase with the parent longwave trough into the Mid-Atlantic and
Northeast, while the southern shortwave likely hangs back into the
Mid-South and Lower MS Valley. The best moisture and instability
lies over portions of the Southeast (where forcing from the
secondary shortwave should still be sufficient for organized
convective activity). The Marginal risk was generally maintained
for this portion of the Southeast (including much of AL/GA with
surrounding portions of East TN, southern MS and the FL Panhandle).
Localized totals of up to 2-3" are generally expected (per GEFS and
ECENS exceedance probabilities), though the inclusion of the full
CAM suite later today will probably push higher-end totals to 3-4"
(still mostly supportive of only a Marginal risk, given associated
3-6 hour FFGs of 2.5-4.0".

...Northeast...

Thunderstorms with heavy rainfall are expected during the afternoon
and evening hours ahead of a northern stream shortwave as MU CAPE
peaks around 1000 J/kg and precipitable water values peak in the
1.25-1.5" range. Sufficient inflow and effective bulk shear is
available for organized convection for much of the period, with
activity expected to be in decline past Tuesday 06z. Hourly rain
totals up to 2" are possible where convection trains, which could
challenge the flash flood guidance across urban portions of the
Mid-Atlantic States. The inherited Marginal risk was maintained.

Churchill/Roth


Day 3
Valid 12Z Tue Apr 01 2025 - 12Z Wed Apr 02 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF SOUTHEAST NEBRASKA, SOUTHWEST IOWA, NORTHEAST KANSAS, AND
NORTHWEST MISSOURI...

A blocking pattern begins to emerge by Day 3, as the aforementioned
shortwaves lift northeastward into Canada with large-scale ridging
quickly builds across the eastern CONUS from the North Atlantic.
Meanwhile, large-scale troughing becomes amplified out West, with a
potent upper-low expected to develop over the Northern Rockies and
Plains (translating across the Rockies from the Pacific Northwest).
While global model suites are in overall good agreement with the
evolution of the synoptic scale, the GFS/GEFS is oddly an outlier
lacking substantial convection with the associated surface low
(which is depicted as a sub 990 mb low from the 00z GFS, ECMWF, and
CMC). Most deterministic solutions depict localized totals of 2-3"
(including the downscaled ECMWF, the UKMET, and the CMC-reg) with
remarkably good spatial agreement for this range, so the inherited
Marginal risk was maintained.

Churchill
$$
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FOUS30 KWBC 010745
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
345 AM EDT Tue Apr 1 2025

Day 1
Valid 12Z Tue Apr 01 2025 - 12Z Wed Apr 02 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE CENTRAL PLAINS & MIDWEST...

Consensus continues to be strong for the overall evolution of a
broad surface cyclone developing in-of the High Plains to Midwest
over the next 24-36 hrs. A strong mid- level trough has ejected
into central CA and will maneuver eastward out of the western
CONUS, aiding in the initiation of a deep surface cyclone across
the Colorado Front Range by later this morning, intensifying
during its life cycle through Wednesday morning and beyond. The
process is manifested through a well- defined axis of difluence
downstream of a robust mean trough/closed-low reflection over the
Rockies, kicking eastward into the High Plains of the Dakotas.
Current deterministic output indicates sub-990mb pressures by later
this afternoon with significant low-level moisture advection
within the lead side of the circulation when assessing the forecast
850-700mb RH field. A textbook warm conveyor belt signature will
mature with a connection based from the Gulf driving warm, moist
air poleward and enhancing a blossoming QPF shield by the time we
reach this evening. The primary focus for heavy rainfall will ensue
after sunset as the initiation of a powerful LLJ across the
Central Plains on the order of 65-75kts will create an axis of
growing low to mid-level shear juxtaposed within a budding warm
sector downstream of the primary circulation. As the surface
cyclone matures, a more defined cold front will develop along the
tail end of the low as it moves into the Plains creating a focus
for convective development as it maneuvers towards the warm sector.

All major deterministic, including the latest 00Z CAMs output indicate
a rapid development of convection across portions of northern KS
into southeast NE advancing east- northeast within the bounds of
the cold front and warm sector of the cyclone. There is also some
growing consensus of a further south and southwest extension of
the convective field within eastern KS down into OK due to the
ejection of a weak mid-level perturbation caught up in the mean
flow that intersects the prolific LLJ bisecting the areas above.
This correlates well with the current ML output that has been
steady with a small sector of convection displaced from the main
line that will ultimately develop over KS into NE and IA.

HREF neighborhood and EAS probs for the primary axis of convection
over northeast KS and points northeast are very much elevated with
a core of 50-70%+ for at least 2" total via neighborhood
probabilities and 40-60% for at least 1" total via a the more
conservative EAS, a testament to a solid overlapping signal for
heavy rainfall within the above zone. A wide swath of 30-50% probs
for at least 2"/3-hrs is also situated within the primary zone of
interest, alluding to modest FFG exceedance probabilities for the
3-hr time frames between 00-12z Wednesday. Further south, the
probabilities are lower, but still within the lower bounds to at
least consider the potential. Latest First Guess Fields have been
steady to include that area across OK and eastern KS and a few CAMs
are worthy of the consideration. These types of synoptic and
mesoscale setups being depicted could offer some surprises due to
the increasingly favorable thermodynamic and kinematic evolutions
forecast within a rapidly improving environment, so to refrain
from missing out on potential, was sure to maintain the previous
MRGL risk with only minor adjustments within the southern and
northern bounds of the risk area attributing to current
probabilities and CAMs signals.

Kleebauer


Day 2
Valid 12Z Wed Apr 02 2025 - 12Z Thu Apr 03 2025

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE LOWER MISSISSIPPI AND OHIO VALLEYS...

The D2 period will represent the initial stages of a prolonged
heavy rain event that will reside over the Lower Mississippi and
Ohio Valleys with a multitude of frontal waves riding along a
persistent quasi-stationary front that will undulate at times when
interacting with the aforementioned surface waves. The general
longwave pattern will become increasingly favorable for a "highway"
of moisture and mid-level impulses to eject northeastward out of
the southern Rockies/Plains and up through the Mississippi and Ohio
Valleys beginning Wednesday afternoon, onward. The consensus among
all ensembles and much of the deterministic fields are the first
wave of the pattern to maneuver over the mid-Mississippi Valley
around the base of a broad trough located over the Plains/Midwest
creating ample surface-based ascent to couple with the powerful
upper jet component situated over the Central CONUS in response to
the evolving pattern the day prior.

At the surface, a cold front will run into a stout western ridge
extension from a surface high located over the Western Atlantic
into the Canadian Maritimes. The pattern essentially comes to a
stalemate thanks to an expected +2 to +3 standard deviation height
anomaly centered over the Western Atlantic. This ridge will counter
the deepening trough over the Central U.S. creating a funneling
affect for deep moisture advection through the Mississippi and Ohio
Valley's, along with ample mid-level impulses that will be preside
over the same areas. The gridlocked setup will create a formidable
moderate to heavy rain event across the above areas with
depictions from guidance indicating a widespread 2-4" with some
areas exceeding 5" increasingly likely within the corridor impacted
by the multitude of convective elements spawning southwest to
northeast in proxy to the quasi- stationary front.

Latest prob fields based within the NBM blend and relevant EC/GEFS
ensembles signal a high likelihood of totals >3" over the span of
18z Wed to 12z Thu with more rain continuing beyond the D2 period.
The maxima is focused within a narrow corridor from central and
northeast AR up through the mid-Mississippi Valley encompassing far southeastern MO, western KY, and southern IN with the probability
for >2" running between 60-80% and >3" settling between 40-60%
without a full implementation of the CAMs into the blend. Rainfall
rates will be generally between 1-2"/hr at peak intensity when
assessing the current HREF/NBM outputs, however, there's a chance
for higher rates located within the southwestern flank of the
stationary boundary (Much of Arkansas up into western KY) as
assessment of the PWAT advection regime signals potential for
localized PWATs exceeding 2" at times during organized convection. Historically, this tends to lead to locally higher rates with
prospects of 2-3"/hr possible, especially when accounting for
intra-hour rates during maturing convection. In all, the setup is
very much conducive for substantial rainfall totals in a span of
12-hrs that will allow for high flash flood concerns within urban
zones and an increasing potential for significant flash and river
flooding outside those areas just due to the overall QPF footprint
anticipated.

This is an increasingly significant setup approaching with
potential for high impacts and life-threatening flash flooding
spanning the course of several days. Be sure to prepare if you live
in a flood zone anywhere from Arkansas, northeast through the
Ohio/Tennessee Valley's. Anyone surrounding will want to monitor
this setup closely as small changes could have heightened impacts
given the forecasted setup.

Kleebauer


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