FOUS30 KWBC 140802
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
402 AM EDT Mon Jul 14 2025

Day 1
Valid 12Z Mon Jul 14 2025 - 12Z Tue Jul 15 2025

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE MID-ATLANTIC STATES...

...Mid-Atlantic Through Northeast...
A cold front slowly advancing from the Ohio Valley will advance
into New England and the Mid- Atlantic states during the evening.
The guidance is in good agreement that convection will develop on a
pre-frontal trough downstream of the front and become numerous
during the afternoon. This will be in response to the accompanying
ascent (through height falls, a potent vort max swinging out of the
Ohio Valley, and low- level convergence) acting upon impressive
thermodynamics characterized by PWs that will exceed 2.25 inches (a
daily record) and MUCAPE of 1000-2000 J/kg. With warm cloud depths
also progged to reach 14,000 ft, efficient warm-rain processes
should dominate all convection this afternoon.

Although storm motions may remain progressive today as 0-6km mean
winds are progged to be angled sharply to the front (some better
training potential farther north into New England), intense rain
rates are expected as reflected by HREF 2"/hr probabilities that
reach 30-50%, suggesting locally 3+"/hr rates are possible. During
storm initiation, motions could be a little slower than once they
become more organized, which would lengthen the duration of any
heavy rain rates, and bulk shear of 20-25 kts could organized cells
into multi-cells, leading to subtly longer and more enhanced
rainfall as well. With extreme rain rates expected everywhere that
develops convection, rainfall could reach 2-4" with locally higher
amounts above 5" possible (HREF/REFS 40-50% chance).

While the CAMS are in good agreement with storms along the pre-
frontal trough pushing eastward, there remains some uncertainty into
pre-trough convective development. If the solutions of the ARW/ARW2
verify, which appear reasonable depicting scattered air-mass type
storms in the region of broad large scale ascent, then these slow
moving storms ahead of the line would enhance the flash flood risk,
and develop the greater potential for the 5+ inches of rain
progged by the neighborhood probabilities. Additionally, the CSU
First- Guess field (both UFVS and non UFVS versions) indicate a 25%
risk area across the I-95 corridor from near Richmond, VA to near
New York City, which is aligned with the highest ECMWF EFI
probabilities as well. Since this heavy rain signature is
consistent among the various ensembles, and will likely occur atop
primed soils from recent heavy rain, an upgrade to a MDT risk was
coordinated with the affected WFOs.

...Florida...
A westward advancing inverted mid-level trough accompanying a
slowly intensifying tropical wave will continue to push westward
today, reaching the east coast of the Florida Peninsula by the end
of D1. Although the primary trough axis will just clip Florida
today, downstream vorticity lobes swinging out ahead of it will
cross the peninsula, leading to robust ascent which will otherwise
be enhanced by upper divergence and a westward advancing sea
breeze. This lift will occur into intense thermodynamics as PWs
surge towards 2.25 inches, which is above the 90th percentile
according to the SPC sounding climatology, collocated with MUCAPE
of more than 2000 J/kg. As the trough axis shifts west, low-level
flow will veer more to the east, leading to enhanced moisture
advection onshore while additionally producing low- level
convergence axes in a region already experiencing impressive deep
layer lift. The result of all of this will be widespread showers
and thunderstorms today, with rainfall rates of 2-3+"/hr.

Coverage across the peninsula will vary considerably based on time
of day today. Overnight (before 12z Monday) and early on Monday,
storms will likely be confined along the Atlantic coast. However, as instability climbs through the day, convection will spread across
the area and then move S/SW on 0-6km mean winds of 15 kts. While
this will keep cells generally progressive, some short duration
training is possible along convergence axes and where any
organization can occur through 20-25 kts of bulk shear. Then late
tonight, generally after 03Z Tuesday, as the trough axis moves
onshore, a secondary enhancement of convection may accompany a
developing surface wave and move back onto the Atlantic coast. Where
repeating rounds or any training can occur, total rainfall of 3-5"
with locally higher amounts (40-60% chance of 5+ inches from the
HREF) possible. This will produce at least scattered flash flood
impacts today, especially across any urban areas.

...Desert Southwest through the Mid-Mississippi Valley...
Complex upper level pattern will lead to another day of scattered
but intense convection, with clusters of locally more organized
activity, from the Desert Southwest through the Mid-Mississippi
Valley. The driver of this activity will be a strung out mid-level
ridge which will maintain a west-to-east oriented axis from Nevada
into Oklahoma, and a secondary ridge over the Southeast. Between
these features, a shortwave trough will be trapped within a col and
move slowly over the Ozarks, while additional shortwave impulses
rotate westward around the equatorward side of the ridge from West
Texas through New Mexico and Arizona. Ascent accompanying these
features will act upon robust thermodynamics to support heavy
rainfall, as PWs rise to 1.75-2.0 inches from the Gulf Coast of
Texas into the Mid-Mississippi Valley, with a secondary maximum
approaching 1.25-1.5 inches in southern Arizona. Additionally,
MUCAPE, especially during peak aftn/eve heating, will rise to 1000-
2000 J/kg across much of the area.

In this environment, the CAMs suggest generally scattered
thunderstorm development, but with locally enhanced coverage and
intensity. Regardless, any cells that develop will likely contain
rainfall rates of at least 1"/hr (generally 30-60% chance), with
local rates of 2-3"/hr likely, especially from Texas into the
Ozarks. Despite the scattered nature of thunderstorms, there may be
two focused areas today:

1) Across the Desert Southwest a potent shortwave undercutting the
ridge will drift southwest into southern NM and AZ, overlapping a
surge of elevated PWs drawing northward from the Rio Grande Valley
this evening. Rainfall rates may touch 1"/hr at times as CAPE
increases, especially where any storms can organize into clusters
through 0-6km bulk shear of 20-25 kts and storms drop SW off the
terrain. The HREF and REFS 24-hr probabilities for 1+" rise above
60%, highest in SE AZ/SW NM, with the HREF indicating a low end
potential (10% chance) for 3" in this same vicinity. Briefly
considered a SLGT risk for this region, but current satellite
suggests cloud cover will be expansive this morning and CAPE may
struggle to regenerate, so the MRGL risk was left although
isolated impacts are likely.

2) The other area will be from the TX Hill Country northeast into
the Ozarks along a decaying stationary front which will help to
focus slow-moving thunderstorms with the aforementioned intense rain
rates this afternoon/evening. Additionally, an MCV noted in
satellite imagery lifting northward from Coahuila, Mexico this
morning, is likely to provide additional focus for ascent across
south-central Texas. Although the CAMs feature a large variation in
QPF amounts and spatial footprint, there is an increasing signal
for heavy rainfall across the Hill Country, which is additionally
supported by low-level PW (from CIRA LPW products) reaching above
the 95th and even 99th percentile between 850-700mb which will be
supported by strengthening winds within that layer (actually the
strongest winds of the column) providing additional lift through
convergence. This region has been exceptionally wet recently as
well (AHPS 7-day rainfall more than 600% of normal) leading to
extremely vulnerable soils and FFG of just 0.25-1.5"/3hrs. This is
also where the ECMWF EFI is 0.6 to 0.7, indicating an increasing
threat for a heavy rain event, which overlaps a SLGT risk forecast
from the CSU first guess field. After coordination with WFO
SJT/EWX, a SLGT risk was added, focused across the TX Hill Country.

...Northern Plains...
Generally flat/zonal 500mb flow aligned along the Canada/United
States border will gradually amplify into a broad trough this
aftn/tonight as a potent shortwave digs out of Alberta. This
evolution will push a wavy cold front southeastward into an airmass
with PWs above the 90th (locally 97th) percentile according to
NAEFS. A piece of this shortwave and its accompanying vorticity
will swing eastward along the front as the low-level baroclinic
gradient strengthens due to a surging southerly LLJ reaching 25-35
kts to enhanced warm air advection. This will draw even more
favorable PWs northward, and where the most impressive ascent
overlaps the favorable thermodynamics, convection with heavy
rainfall will result. 0-6km mean winds of 20-30 kts suggest storms
will be progressive, but also track parallel to the front which
indicates a training potential. Additionally, some modest
organization is possible which could help enhance rain rates to 1-
2"/hr, especially later this evening. 6hr/5yr RI exceedances peak
this evening as the LLJ ramps upward, suggesting at least an
isolated excessive rainfall/flash flood risk later today.

Weiss
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FOUS30 KWBC 150809
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
409 AM EDT Tue Jul 15 2025

Day 1
Valid 12Z Tue Jul 15 2025 - 12Z Wed Jul 16 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR THE FLORIDA
PENINSULA, PARTS OF THE MID-ATLANTIC, THE UPPER MIDWEST, SOUTHEAST
ARIZONA, AND CENTRAL TEXAS...

...Florida...
Potent and intensifying mid-level trough positioned just east of
the FL peninsula tonight will translate slowly westward beneath a
ridge positioned to its north. As this feature tracks back over the
Gulf on Tuesday, a surface reflection is likely to develop (even
if not Tuesday, eventually, and NHC has a 40% chance of
development) which will enhance ascent. This feature will be
accompanied by a pool of exceptional PWs of 2.25 to 2.5 inches,
approaching +3 standard deviations above the climo mean, and
elevated MUCAPE of 1000-2000 J/kg. As this tracks across the
peninsula Tuesday, convection is expected both in the vicinity of
the mid-level center, but also along any convergence bands that
occur within the pivoting 850mb inflow. Due to the robust
thermodynamics, rainfall rates of 2-3"/hr are expected (50-70%
chance of 2+"/hr according to HREF neighborhood probabilities),
which through generally slow and chaotic storm motions will result
in axes of 3-5" of rain, highest along the western coast or beneath
the core of the mid-level center. This rain will occur atop areas
that are more vulnerable due to heavy rainfall on Monday, and the
SLGT risk remains with only modest cosmetic adjustments.

...Northern Rockies through the Upper Midwest...
Expanding trough digging across the Northern Rockies and Northern
Plains will drop steadily southward Tuesday in response to a potent
shortwave digging out of Alberta, Canada. As this impulse gets
embedded into the more pinched westerlies downstream, it will shed
spokes of vorticity across the region to help enhance ascent
already intensifying through height falls. This evolutions will
also drag a cold front southward, but this front will oscillate
north and south through D1 in response to the aforementioned shortwaves/vorticity spokes interacting with its baroclinic
gradient. In fact, the latest guidance suggests that two distinct
waves of low pressure will develop along this front and track
eastward, leading to more focused heavy rain from convection within
otherwise scattered thunderstorms.

Although the broad MRGL risk remains, there appears to be two
focused areas for heavier rainfall. The first is in a SW to NE
oriented axis from Nebraska through the Arrowhead of Minnesota.
Here, southerly 850mb inflow will surge out of the Central Plains at
20-25 kts and impinge into the front itself. This will additionally
draw impressive thermodynamics (MUCAPE above 2000 J/kg and PWs above
1.75 inches, or the 97th percentile according to NAEFS) northward
into the front. Where the maximum ascent occurs atop these
thermodynamics, widespread convection with heavy rainfall rates of 1-
2"/hr are expected, and these storms have a high potential to train
SW to NE along the front due to 0-6km mean winds that are
progressive at 10-20 kts, but parallel to the boundary. Where these
elements train, HREF 3-hr FFG exceedance probabilities peak above
40%, and the inherited SLGT risk remains.

A second region of heavier rainfall is expected across MT. Here,
persistent westerly mid-level flow atop the front combined with
sloped frontogenesis will drive nearly continuous periods of
rainfall. PWs in the region will be elevated above the 90th
percentile according to NAEFS (0.75 to 1 inch), but accompanying
instability is minimal. This suggests that most of the rainfall
rates should be 0.5"/hr or less, so despite the impressive ECMWF EFI
signal for heavy rain (EFI > 0.9), the excessive rainfall risk
remains MRGL even if a few locations approach 3 inches of total rainfall.

...Mid-Atlantic and Southeast...
Broad mid-level ridging centered off the Carolinas will continue
to extend back to the west as far as the Southern Plains. This will
persist the moist and unstable environment that has been plaguing
much of the east for several days now, resulting in another day of
scattered to numerous thunderstorms. On Tuesday, the focus for
convection will likely be along the decaying front which will drag
slowly southeast as it wanes, reaching from the Ozarks to the Mid-
Atlantic states, although with some oscillation north-south
expected at times. Along this boundary, generally SW flow emerging
from the Southern Plains will drive periodic impulses northeast,
interacting with the front and providing locally enhanced focused
ascent for convection. With PWs consistently above 2-2.25 inches
and MUCAPE 1000-2000+ J/kg, storms that develop will be capable of
producing efficient rain rates in excess of 2"/hr pretty much
anywhere across the region.

In general, coverage should be scattered and not support more than a
MRGL risk of excessive rainfall. However, some locally focused
convection beneath an impulse and aided by upslope 850mb inflow
could produce heavier rainfall from the Central Appalachians into
the Mid-Atlantic states. The guidance has continued to trend just a
bit south overnight with the axis of heaviest rainfall, but with the
front wavering through the day, and a general noted northward bias
in the convection on Monday (compared to progs), changes to the
inherited SLGT risk were modest and focused over more vulnerable
areas from recent heavy rainfall.

...Southwest...
The monsoon will become more active today as the elongated mid-
level ridge over the Desert Southwest weakens in response to a
potent vorticity maxima/shortwave drifting around its periphery.
This feature will traverse westward beneath the ridge, crossing
from the High Plains of NM through southern Arizona, and act upon
an increasingly moist and unstable environment. PWs are progged to
surge to as high as 1.25-1.5 inches, highest in southern AZ,
coincident with a ribbon of MUCAPE of 1000 J/kg lifting northward
as low-level flow surges out of the Rio Grande Valley and Mexico.

The high-res CAMs are generally modest with convective coverage on
Tuesday, but the recent HRRR and RRFS are much more aggressive with
simulated reflectivity, and are likely the better solutions
conceptually for the environment. As storms develop, generally in
the higher terrain first, they will be slow movers with rain rates
of 0.5-1"/hr. However, during peak instability, storms will congeal
and feature at least subtle organization beneath the shortwave as
bulk shear rises to 20-25 kts and storms coming off the terrain will
move generally west-southwest and feature rain rates that may
briefly exceed 1"/hr. The inherited SLGT risk is maintained and
adjusted subtly.

...Central Texas...
850mb LLJ surging to 20-25 kts from the south and up through the
Rio Grande Valley will again support overnight convection
persisting into the new D1 period (after 12Z Tuesday). This will be
accompanied by a shortwave/vorticity maxima lifting northward and
favorable instability of more than 1000 J/kg to support at least
scattered thunderstorms. The high-res CAMs are not aggressive with
convective coverage after 12Z Tuesday, but even isolated activity
will contain rain rates that could exceed 2"/hr, and Corfidi
vectors that are aligned anti-parallel to the mean wind, combined
with favorable upslope into the Hill Country on southerly winds
could result in backbuilding/nearly stationary storms at times.
With the area remaining extremely vulnerable due to repeated rounds
of heavy rain in the past week, (FFG as low as 0.25"/3hrs) the
SLGT risk was tailored but continued into Tuesday.

...Mid-Mississippi Valley...
Weak impulses/MCVs embedded within the mean SW to NE mid-level
flow will lift out of Texas and interact with a weakening
stationary front over the Mid-Mississippi Valley. ALthough in
general, forcing for ascent will be modest, it will be locally
enhanced where these impulses move atop the surface convergence
associated with the front itself. Intense thermodynamics will
remain across the area reflected by PWs approaching or exceeding 2
inches collocated with MUCAPE above 1000 J/kg to support rainfall
rates of 1-2"/hr in convection. Mean winds of 10-15 kts suggest
individual storms will be progressive, but some weak organization
and some training along the front could enhance the duration of
heavy rainfall. This appears most likely in the vicinity of
southern IN where moisture confluence maximizes, creating a locally
greater excessive rain risk, but the MRGL risk remains for
isolated impacts today.

Weiss
$$


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FOUS30 KWBC 160816
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
416 AM EDT Wed Jul 16 2025

Day 1
Valid 12Z Wed Jul 16 2025 - 12Z Thu Jul 17 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE MID-ATLANTIC STATES, THE CENTRAL PLAINS, AND THE UPPER MIDWEST...

...Central High Plains through the Great Lakes...
Return flow around a broad mid-level ridge centered off the
Atlantic coast will continue to result in a plume of exceptional
moisture and instability rotating across much of the CONUS. Today,
this plume of thermodynamics will stretch from Texas into the Upper
Midwest and then into New England, where PWs of 1.5 to 2.25 inches
overlapping pools of MUCAPE exceeding 2000 J/kg will reside. Into
this plume, a dissipating stationary front will drop southeast,
while a secondary front approaches from the NW in response to
subtle height falls in response to broad but increasing troughing
over the Northern Plains. This will result in squeezed mid-level
flow from WSW to ENE from Texas into New England, through which
multiple shortwaves will traverse along the boundary to
additionally enhance ascent. Although much of the area will
experienced scattered convection, there is likely to be an axis of
enhanced organization from Kansas into Wisconsin.

In this region, multiple MCSs driven by connectively enhanced
shortwaves will move across these areas with focused heavy rainfall,
aided by waves of low pressure which may develop along the front.
Although there continues to be some latitudinal and longitudinal
spread with the placement of these MCSs which will be the primary
driver of the flash flood risk, a slowly veering 30-40kt LLJ
emerging from the Southern Plains will provide the focus for
development through convergence and isentropic lift. The models
suggest potentially two foci for heaviest rain, one in Kansas and a
second axis from southern MN into WI, but anywhere across this
region could experience short term training through Corfidi vectors
that are aligned to the mean wind and the front (MN and WI) or anti-
parallel to the mean wind (KS). With rain rates likely reaching 1-
2"/hr, if not locally higher, this could result in instances of
flash flooding and the inherited SLGT risk was modified for new
guidance to cover the highest probabilities for 3" and locally 5" today.

...Ohio Valley into the Mid-Atlantic...
Farther east into the thermodynamic plume mentioned above, a
secondary maxima of heavy rainfall is likely from Ohio into
Pennsylvania and surrounding areas. This is where a shortwave is
progged to track overhead during peak heating and maximum
instability. This will not only drive enhanced ascent, but also
accelerate bulk shear to 30-35 kts which will force better storm
organization. 850mb inflow across this area will also strengthen,
potentially reaching 30-35 kts which will be 1.5 times the mean
0-6km wind, a signal for strong convergence. Although storms that
develop should remain progressive to the east, slower storm motions
during convective initiation are also possible. Regardless of the
exact behavior, multiple rounds are likely in many areas, and each
one will rainfall rates of around 2+"/hr (20-40% chance), leading
to total rainfall of 2-4" with locally higher amounts possible
(10-20% chance of 5" in both REFS and HREF, despite latitudinal
placement differences.) This falling atop saturated soils from
recent heavy rainfall will likely result in instances of flash
flooding once again today.

...Gulf Coast...
Invest 93L exiting the northern Florida peninsula this morning
will drift westward into the northern Gulf on Wednesday. The
accompanying mid-level inverted trough/tropical wave will be forced
due west as it remains south of an elongated ridge extending from
the Atlantic Ocean. There continues to be quite a bit of spread of
intensity of the accompanying surface reflection to this feature
(and NHC continues a 40% chance of development) but the track
guidance has converged moving just south of the coast through the
next few days. Regardless of the exact track and development of
this system, the accompanying tropical moisture plume (PWs 2.25 to
2.5 inches, as much as +3 sigma according to the GEFS) will spread
onshore to support showers and thunderstorms with heavy rainfall
rates of 2-3"/hr. There continues to be uncertainty into how far
north any of this moisture will spread due to subsidence/dry air
beneath the ridge to the north, but guidance has begun to focus a
relative maxima across southeast LA, and potentially as far east as
Mobile Bay, AL. In this corridor, both the HREF and REFS
probabilities for 5"/24 hrs exceed 25%, and the inherited SLGT risk
has been cosmetically adjusted for this area, embedded within a
larger surrounding MRGL risk.

...Desert Southwest...
Active convection is likely again today across the Southwest as
the mid-level ridge weakens and weak impulses, some of which are
convectively enhanced by thunderstorms from Tuesday, move across
the region. PWs are expected to continue to be above 1.25", highest
across southern AZ, but with a slow decrease in intensity and
coverage of this PW plume. Additionally, probabilities for CAPE
exceeding 500 J/kg are lower and confined east of the greatest
moisture today, indicating that coverage and intensity of
thunderstorms should be less than what occurred Tuesday. Despite
that, convection should still be relatively widespread, but
possibly displaced north of previous activity, although any weak
remnant MCVs could enhance local ascent leading to local flash
flood impacts, most likely should any thunderstorms with 0.5"/hr
rain rates track across burn scars or sensitive terrain.

Weiss

$$
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FOUS30 KWBC 170814
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
414 AM EDT Thu Jul 17 2025

Day 1
Valid 12Z Thu Jul 17 2025 - 12Z Fri Jul 18 2025

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR THE LOWER
ATCHAFALAYA BASIN IN SOUTH-CENTRAL LOUISIANA...

...Northern Gulf Coast...

A highly disorganized tropical disturbance continues tracking west
across the far northern Gulf this morning, with a center off the
coast off Mississippi as of the time of this writing. This
disturbance is responsible for a larger area of thunderstorms well
west of the center, moving across southern Louisiana. The storms
will turn southward and move out into the Gulf through the morning.
More widespread, albeit widely scattered thunderstorm activity
will develop today as the center moves into southeast Louisiana.
Much of the strongest activity is expected to focus west of the
center of circulation, but will push westward as it does so.

Beyond ample atmospheric moisture is in place, with New Orleans
sounding measuring PWATs of 2.27 inches from the 00Z sounding.
Thus, while the storms ongoing over Louisiana are largely sticking
to rainfall rates under 1.5 inches per hour...with ample
instability developing with daytime heating today, any storms that
form will have more than enough instability and moisture available to
locally produce rainfall rates in excess of 3 inches per hour.
However, since the storms will be moving westward, any one location
will see rainfall rates that heavy for only a short time. With FFGs
near their average at 3.5 to 4 inches per hour over much of
Louisiana, it will take repeating rounds of storms to exceed FFGs
enough to induce significant flash flooding. This is likely to be a
high bar to overcome in most areas, as despite the ample moisture
and instability, the forcing associated with this weak, slanted,
and overall disorganized low is very lacking in most areas.

The Moderate Risk includes the Lafayette area and the Lower
Atchafalaya Basin in large part because of the V-shaped nature of
the river basin, heavy rain could funnel into flood prone areas
quickly if the heavy rain over the basin is persistent enough. In
coordination with LCH/Lake Charles, LA forecast office, the
Moderate Risk previously in the Day 2/Friday period was transferred
to today, as the likelihood for more organized convection across
Louisiana will be significantly greater today, resulting in a
greater coverage of heavier rain today than is now expected
tomorrow/Friday.

The surrounding Slight Risk area extends from the far western
Florida Panhandle west along the coast to the Texas border. Many of
the same thunderstorms impacting southeastern Louisiana will
continue west into southwestern Louisiana before dissipating,
resulting in the continuation of the Slight Risk. Any heavy rain
will have to contend with very high FFG values across all of the
Louisiana coast. Meanwhile further east from coastal Mississippi to
the far western Florida Panhandle, the combination of urban areas,
and southerly onshore flow off the Gulf will support a northward
convective motion, favoring training in these areas.

...Ozarks to the Ohio River Valley...

A stalled out front over this region acting as a barrier between
much drier air to the north over the Great Lakes and a hot and very
humid air mass from the Ohio Valley south will act as a focus for eastward-moving complexes of showers and thunderstorms to develop
and push quickly east as new thunderstorms from to their west. This
will occur over a long line from the central Plains to the central
Appalachians this afternoon and tonight. Persistent southerly flow
of moisture-laden air will support numerous thunderstorms occurring
over these areas today as that southerly flow runs into the stalled
out front and turns eastward. While portions of the Slight Risk
area have seen more prior rains than others...during the day today
expect PWATs routinely over 2 inches to support thunderstorms
capable of up to 3 inch per hour rainfall rates. These heavy
rainfall rates will be offset by their fast movement, but given the
stationary front in place directing all the storms along the same track...training is likely.

The Slight Risk area was expanded a bit into southeastern Virginia
and northwestern North Carolina with this update, in coordination
with RNK/Blacksburg, VA forecast office. Elsewhere few changes have
been made since the pattern remains steady state.

...Northeastern New Mexico and Adjacent Areas...

Only a very modest eastward shift was made to the previous Slight
Risk area, which is largely centered over northeastern New Mexico,
a southerly LLJ running into both terrain and a thermal low will
act as a focus for rather fast moving thunderstorms to track ESE
out of CO/NM and eventually into the OK/TX Panhandles. Like the
other higher risk areas, southerly flow of moisture will support
backbuilding and additional convective development behind the
initial round of storms. Training over flood-sensitive areas may
result in widely scattered instances of flash flooding this
afternoon into this evening.

Wegman


$$
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FOUS30 KWBC 210812
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
412 AM EDT Mon Jul 21 2025

Day 1
Valid 12Z Mon Jul 21 2025 - 12Z Tue Jul 22 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR MUCH OF
KENTUCKY, TENNESSEE, AND PORTIONS OF THE SOUTHERN APPALACHIANS...

...Southern Ohio Valley into the Southern Appalachians...

Evolving pattern with a seasonally strong surface ridge to the
north will aid in pressing the persistent quasi-stationary boundary
across the Mid Atlantic and Ohio Valleys to the south leading to a
degrading precip field north of the front, but maintaining
convective posture along and south of the boundary. A panoply of
weak shortwave perturbations will be rippling through southern Ohio
Valley into the southern Mid Atlantic on Monday with expected
diurnal destabilization over much of KY/TN into southwestern VA
leading to another period of scattered to widespread convective
flare ups in the prevailing warm sector. A relatively buoyant
environment in place across the above areas will promote locally
heavy downpours capable of rates >2"/hr, something that has been
customary within this persistently moist airmass lingering from the
western fringes of the Western Atlantic ridge. Expect PWATs to hang
within the +1 to +2 standard deviation range across the above areas
with the latest 00z HREF mean MUCAPE to hover between 1000-2000
J/kg for much of the Southern Appalachians with 2000-3000 J/kg
presence across much of KY and TN. The elevated CAPE indices
coupled with the moisture rich environment of >2" PWATs will lead
to scattered instances of flash flooding, especially over those
terrain focused areas of eastern KY/TN into southwest VA where
multiple instances of heavy rainfall have led to a series of FFW's
being issued the past several days.

00z HREF neighborhood probs remain high (>60%) for at least 1" of
rainfall with >2" running between 40-60% over a large area
encompassed by low FFG indices for 1/3/6hr increments. The
positioning of the front will be factor for the northern periphery
of the greatest convective reflection in the setup, as well as a
focus for anchored cores that could relish on the capability to
drop between 2-4" of rainfall in spots as depicted within the
latest 00z CAMs suite. Considering both the probabilistic and
deterministic maxima being depicted within the hi-res suite, there
was enough consensus to maintain general continuity of the previous
SLGT risk inheritance with a southward shift in the risk area
overall to reflect the latest trends of frontal positioning and
convective output within the CAMs.

...Southern Mid Atlantic into the Southeast...

Scattered strong convective cores will be capable of heavy rainfall
in pretty much any area within the bounds of southern VA down
through the Carolina's into the Southeastern CONUS. The best
threats for more organized heavy convective regimes will be located
over eastern NC and the north-central FL Peninsula. The two
patterns will not be related in any way, but they do share an
element of robust instability and a foci for convection along a
surface based front/boundary in the form of a cold front (NC) and
surface trough (FL). FFG's within each area are still pretty high
overall for all 1/3/6hr indices, so the threat for more widespread
flash flood concerns is lower, but still worthy of a risk
considering the environmental factors in play. Elevated probs for

3" locally (50-70%) are sufficient for those flash flood concerns

for each area respectively. However, a sharp decline in the
prospects for >5" really mutes the higher risk potential and keeps
the threat within the MRGL threshold. As a result, there was very
little deviation from the previous forecast with only minor
adjustments over the Southern Mid Atlantic coast near the VA
Tidewater. MRGL risk remains in effect.

...Southwest U.S...

The southwestern U.S will maintain a persistent convective posture
with a defined monsoonal axis across NM/AZ with a sharp cutoff in
deeper moisture as you move closer to the Colorado river Basin.
Isolated stronger cores will lead to threats of flash flooding just
about anywhere over the two respective areas with emphasis on those
places dealing with remnant burn scars and complex terrain which
exacerbate flash flooding impacts. Strongest signal for heavy rain
in the prob fields remains parked over southeast AZ with the
Huachuca Mtns. the likely beneficiary of slow-moving thunderstorms
and QPF maxima >1" during time frame of impact (18-03z). A pretty
stable element this time of year with a generally seasonal pattern
in place. This is more than enough to constitute a MRGL risk
issuance given the setup.

...Northern Plains through Upper Midwest...

Two-part convective episode over the northern tier of the CONUS
will lead to a few areas seeing repeated heavy rainfall prospects
in the D1 time frame. The first of which will be the migration of a
complex out of the Dakotas into the Red River/Bois de Sioux basins
that border ND/SD/MN in the early portion of the period with
locally heavy rainfall in wake of the passing complex. Still some
discrepancy on the eastward extent and residual QPF magnitude that
will be produced by the complex, but the pattern generally favors a
weakening component over the area above, so perhaps the threat is
on the lower end for flash flood concerns in the first 6hrs of the forecast.

The second time frame of interest will arise over the course of the
following evening as an approaching trough axis across the PAC
Northwest will lead to an increasingly diffluent pattern downstream
of the mean trough, promoting favorable large scale ascent from
eastern MT up into the Dakotas. A series of smaller shortwaves will
propagate northeast into the region after 00z with convective
initiation most likely further west with more question marks on the
maintenance of convection as you step eastward. There's a mixture
of results within the CAMs output for whether the pattern evolves
in such that eastern ND into MN gets put into play for heavy
rainfall overnight Monday into early Tuesday, or is a majority of
the pattern only aligned within eastern MT into ND. The split in
guidance has relegated the signal within the EAS to a paltry <10%
for >1" in the 6hr period between 00-06z Tuesday, but we do see an
uptick in the 06-12z Tuesday window, so perhaps it could be more of
a timing of the convective pattern moving downstream with less
focus on discrete activity prior to the advancing convective
complex. The general rule of thumb for these types of patterns is
favoring a lower risk until there's a greater consensus on what
could transpire. This works well within the area of interest due
to modest FFG indices in place and FFG exceedance probs remaining
on the lower end. A broad MRGL risk is in place for the
aforementioned areas with the greatest concerns across the eastern
Dakotas and eastern Montana.

...Pacific Northwest...

Combination of a weak upper low presence over southwest Canada and
the approach of a more robust shortwave trough into the
Northwestern CONUS will lead to focused areas for isolated flooding
concerns within the terrain of northeast OR and the Washington
Cascades. Signals for locally >1" of rainfall are >70% in each
respective locale, but signals in the deterministic are still
spotty in the grand scheme. The pattern is just conducive for these
localized heavy rain prospects in complex terrain and burn scar
remnants located over northern WA state. Weak IVT advection into
the region along with favored large scale ascent downstream of the
approaching trough should lead to periods of convection during the
height of the convective time frame (18-06z). The signal remains
low-end, but enough to warrant two small MRGL risks over the
aforementioned areas.

Kleebauer
$$
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FOUS30 KWBC 220809
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
409 AM EDT Tue Jul 22 2025

Day 1
Valid 12Z Tue Jul 22 2025 - 12Z Wed Jul 23 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE UPPER MISSISSIPPI VALLEY, SOUTHWEST AND SOUTHEAST...

..Northern Plains/Upper Midwest...

Regional radar mosaic across the Northern Plains depicts a
migrating cluster of thunderstorms over the Dakotas with the proxy
of the convective complex along the ND/SD border. Mean storm
motions continue to point to the complex of thunderstorms migrating east-northeast with heavy rainfall likely to be impacting portions
of eastern ND and far northeast SD into MN by the turn of the new
D1. This complex will likely draw some attention for flash flooding
by itself, but the environment will be somewhat favorable for the
first half of the D1, so the threat will likely be more isolated
with the best chance occurring in any urbanized settings. Majority
of this heavy precip will likely fall north of I-94 in MN with the
Minneapolis metro unlikely to see much of any impacts. The period
becomes more favorable for heavy rain prospects as we move into the
second half of the forecast as a stationary front currently
analyzed over IA/IL into SD will lift northward through the
afternoon with an appreciable advection of deep layer moisture
priming the environment for the following evening. Surface low over
the High Plains will slowly advance through SD during the forecast
period with a cold front dropping steadily out of Canada with eyes
on the Upper Midwest by the end of the D1. The proxy of the warm
front and advancing cold front will lead to a tight window of
enhanced sfc-850mb convergence within a formidable pool of moist,
unstable air positioned across the eastern Dakotas through much of
MN/WI. PWATs between +2 and +3 deviations will be present over the aforementioned areas with values >2" likely as we move beyond 00z
Wed. LLJ initiation across the Upper Mississippi Valley will help
trigger an area of heavy convection across the Dakotas which will
eventually migrate eastward through the Red River basin into the
northern half of MN.

As of this juncture, the greatest threat for heavy rainfall >2" is
likely over southeast ND, far northeast SD, and adjacent areas of
northwestern MN with an eastward expansion over the central portion
of MN (St. Cloud area). 00z HREF and REFS neighborhood
probabilities for >2" are between 80-90+% for these locations with

3" (60-80%) and >5" (20-35%) well within a reasonable depiction

for a widespread flash flood threat in that area of the northern
CONUS. HREF EAS probabilities for >1" are also robust with 70-90%
for >1" and 40-60% for >2" situated over those same areas, a
testament to the growing consensus within the CAMs window as we
move closer to the event. This aligns very well with the EC AIFS
Ensemble mean QPF output of 1.25-1.5" in that corridor, a very
strong output when you take into account the traditional low bias
from the AIFS in general.

The FFG's located across central MN are small deterrent for any
appreciable risk upgrades as the threat targets places where
1/3/6hr indices remain a little high compared to areas a bit
downstream and further south. Despite those indices, multiple flash
flood warnings are increasingly likely over southeast ND, northeast
SD, and central MN as we step through the evening, especially with
a growing threat of training and back-building as proposed by the
weakening Corfidi Upshear vectors in the CAMs as we move into the
evening. This makes sense as the mean flow becomes parallel to the
boundary with the approach of the front to the north.

There is some chance this setup nudges north as the mid-level ridge
to the south will truly flex and the warm front progression should
migrate pretty rapidly to the north through the afternoon and
evening, especially with the added nose of LLJ structure positioned
to the south. Where this ends up is the ultimate delineation point
of where training could occur and have the highest prospects for
flash flooding. For now, a high end SLGT is forecast over that
corridor positioned over ND/SD/northwest MN with an eastward
extension through central MN prior to the Arrowhead. Pending
forward propagation speed of the nocturnal convection, the risk
could evolve further downstream prior to the end of the D1 period,
so it will be something we will monitor closely. In any case, the
SLGT risk still runs through portions of the Arrowhead into
northwestern WI back into those favorable areas to the west.

...Southeast...

Elevated PWATs and instability across the Southeastern CONUS will
maintain a posture of widely scattered thunderstorms capable of
locally enhanced rainfall rates between 2-4"/hr that could spur
flash flood prospects through the course of the daytime hrs. A
weak surface reflection along the SC coast with a weak quasi-
stationary front aligned west to east across the Southeast will
lead to enhanced regional convergence that could allow for slow-
moving heavy thunderstorms to train over any area in proxy to these
features for a few hrs. These are the types of setups that can
provide a sneaky 4-7" maxima in any given location, especially
near the low pressure center along the Carolina coastal plain.
Surface trough extending off the southern flank of the low will
bisect southeast GA down through northern FL with guidance
consistently pinning a more defined heavy precip axis within the
confines of this area. FFG's remain very high across that specific
area, so the threat for widespread flash flooding is very low,
especially when considering the probabilities for >5" are still
running <25% for a majority of that region, a signal necessary for
more appreciable impacts to occur in these zones. 00z HREF
neighborhood probs for >5" are higher than previous forecasts for
the coastal Carolina's with the max probs (30-45%) located from
Morehead City, NC down through Charleston, SC. Multiple population
centers are encompassed in that zone, the most likely locations to
see any flash flood prospects due to urbanization factors. EAS
probabilities for >1" are also pretty elevated over the Upper SC
coast (>50%) with a modest output over the area referenced above.
The synoptic and thermodynamic evolution support a strong coastal
convergence pattern, especially with the afternoon sea breeze
during the life cycle of the surface low, so the upgrade to SLGT
from the last forecast update maintains merit. Considering the
current signals, there was no reason to deviate from the previous
forecast, so the SLGT risk remains due to continuity.

...Southwest...

Another period of monsoonal type convection will enhance localized
flash flood prospects across eastern AZ and much of NM/CO.
Persistent moisture advection along the western flank of a ridge
positioned across the Mississippi Valley will be the driver for the
threat as scattered to widespread showers and thunderstorms will
litter the Southwestern CONUS up into the Central Rockies by
this afternoon, carrying through the evening hrs. Any area within
the confines of the above regions will have a threat for impacts
due to convective cores likely producing rates >1"/hr with upwards
of 2"/hr in the strongest cells. Areal QPF average is generally
between 0.25-0.75", but neighborhood probabilities for >1" over
eastern AZ into NM/CO are well above 70% with >2" probs running
between 40-70% over the more terrain favored areas in both
locations. The most prominent signal for rainfall eclipsing 1"
aligns within the Sangre de Cristos and the eastern side of the
Mogollon Rim near the AZ/NM line. These are the most likely
locations to see heavy rainfall and heightened flash flood
prospects this period with the best chances over any remnant burn
scars. Mean storm motions will be generally weak, so any convective
cores will run the chance of impacting the same areas for multiple
hours before collapsing or moving away from their initiation
points. A broad SLGT risk encompasses much of NM, southwest TX, and
southeast AZ with a bit of an extension into CO along the Sangre de Cristos.

Kleebauer
$$
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FOUS30 KWBC 230811
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
411 AM EDT Wed Jul 23 2025

Day 1
Valid 12Z Wed Jul 23 2025 - 12Z Thu Jul 24 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE UPPER MIDWEST...

...Upper Midwest...

Increased confidence in heavy rainfall is forecast across a good
portion of the Upper Midwest with the latest 00z HREF mean QPF
distribution heavily focused over east-central MN across into
northern WI and the western Michigan U.P through the period.
Expectation is for an initial round of convection forming upstream
over the Dakotas into northwestern MN, migrating east-northeast
within the general mean flow the first 6 hrs of the forecast, a
carryover from the previous D1. Isolated flash flood prospects
will be feasible during this initial wave of precip, but the
pattern takes a turn for potentially higher impacts as the surface
cold front to the north begins pressing further southeast through MN/WI.

Expecting a secondary cluster of thunderstorms to develop
over south-central MN up into northern WI in the early afternoon
hrs., spurred on by a strong theta_E advection regime forming along
and south of the cold front as it begins to fan out more west-
southwest to east- northeast once down near the latitude of
Minneapolis-St. Paul. 00z CAMs are bullish on a broad development
of heavy thunderstorms within the confines of the front with
relatively slow cell motions thanks to the mean flow aligning
parallel to the boundary. A deep moisture presence running between
2-3 standard deviations above normal and wet bulb zero heights
between 13.5-14k ft MSL will enable more efficient warm rain
processes with embedded convective element, an environment
suitable for rainfall rates between 1-3"/hr with some intra-hour
rate potential >4"/hr at times as signaled within some of the
individual deterministic. HREF neighborhood probabilities took a
larger step into more robust depictions of the potential with the
latest >3" signal now firmly between 50-70% from east-central MN
across into north-central WI. This alignment also includes the
greater Minneapolis metro and areas along and north of I-94 within
both MN/WI. This area is one of the more prone spots in the
northern CONUS for flash flooding due to the urban footprint and
locally higher run off capabilities. This signal is prevalent for
much of northern WI with convection basically aligning downstream
and prevailing through much of the afternoon and evening before the
front finally sweeps through and carries the threat more into WI
and the Michigan U.P.

There's growing concern of the upstream evolution also becoming
more suitable for widespread convective development generated by
the ejection of a stronger mid-level shortwave into the Central
Plains providing ample ascent within the diffluent area downstream
of the mean trough. CAMs are in and out on the proposed convective
evolution, mainly spatial coverage with some of the CAMs very
bullish which would exacerbate precip potential downstream over NE
into southeastern SD and southern MN/northern IA. This is setup can
tough to figure out at leads, but the mass fields involved are very
much capable of producing a secondary area of heavy precip, even
bordering on significant if you believe some of the hi-res deterministic.

Overall, the combination of favorable thermodynamics and upper
forcing brought on by right-entrance region dynamics from a
strengthening upper jet over Canada will combine to produce
widespread heavy rainfall with a lean towards locally significant
impacts, especially along and north of the I-94 corridor. Totals
between 2-4" with locally as high as 6" are forecast within the
Upper Mississippi Valley up towards the shores of Lake Superior. As
a result, a high end SLGT is forecast from south-central MN and
points northeast, including; Minneapolis/St. Paul, Duluth, Eau
Claire, and the western Michigan U.P. SLGT risk encompasses much of
the Upper Midwest, extending back to the southwest through parts of
the Central Plains thanks to the prospects of a secondary heavy
convective episode that could very well gain more traction as time moves on.

...Florida and the Coastal Southeast...

The active pattern across the Southeast CONUS will continue through
Wednesday with a generally smaller convective footprint compared to
the previous period, but enough to warrant a continued MRGL risk
for locally heavy rainfall. Weak upper trough carrying a formidable
tropical airmass will pivot eastward along the Central Gulf coast
leading to PWATs encroaching 2.25-2.5" consistently from LA over
into the northern half of the FL peninsula. Ascent pattern is
fairly tame with the lack of sufficient jet dynamics, but the
combination of a weak surface reflection migrating southwest from
off the GA coast into the northeast portion of the Gulf will aid in
some enhanced low-level convergence capable of heavy convection
firing and maintaining foothold over places like the northern FL
peninsula and along the immediate Central Gulf coast. Signals are
relatively weak for prospects of >5" (<20%), but there is a decent
enough threat for upwards of 5" which is more than feasible
considering how little effort it will be for any convective
elements to produce 2-3"/hr rates given the favorable buoyancy and
deep moisture presence. Any cells that train or hold ground for any
length of a few hrs. could spell for locally significant rainfall
which could induce flash flood concerns, even away from urban
centers. The previous MRGL risk was maintained with only minor adjustments.

...Central and Southern Rockies into High Plains...

Another active period on tap with scattered to widespread
convective development anticipated across the Central and Southern
Rockies through the adjacent High Plains on Wednesday afternoon and
evening. PWATs remain very high (90-97th percentile according to
NAEFS anomalies) across the central High Plains with a bit less a
deep moist axis in-of the Rockies. Even with the less emphatic
signature over the terrain, a slew of smaller mid-level
perturbations within a shortwave trough located over the Front
Range, as well as increasing upper ascent ahead of a deeper upper
trough centered off CA will allow for ample convective initiation
across NM up into CO with a consensus on the greatest coverage
along the Continental Divide. The aforementioned shortwave over the
Front Range will be the disturbance that kicks off yet another
convective cluster over northeast CO with advancement to the
northeast as it follows the mean flow. A relatively good agreement
on a regional max over that area of northeast CO into southern NE
with neighborhood probs running between 40-70% for at least 2" in
this corridor. FFG's in these areas are somewhat high compared to
areas well downstream, so the ability to take a decent hit of heavy
rainfall is better leading to lower chances for widespread flash
flood prospects. Still, it's an area to monitor for short term
upgrades if the signal becomes more prolific for higher totals. NM
coverage will be less than the previous period, so isolated to
widely scattered flash flood concerns lean more to a broad MRGL
risk as well with the extension into CO.

Kleebauer
$$
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FOUS30 KWBC 240804
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
404 AM EDT Thu Jul 24 2025

Day 1
Valid 12Z Thu Jul 24 2025 - 12Z Fri Jul 25 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM THE CENTRAL
AND SOUTHERN HIGH PLAINS INTO THE MIDWEST...

...High Plains into the Midwest...

Active pattern across the Central CONUS continues through Thursday
with another round of heavy convection likely in proximity to a
steady moving cold front from the north. At the surface, cold front
analyzed over the Northern Plains and Upper Midwest will make
headway to the south and southeast with a greater latitudinal push
west of the Mississippi due to a strong sfc-500mb ridge axis
nestled across the Southeastern U.S. The general southwest to
northeast alignment will be precursor to the expected mean cell
motions for the period with emphasis on convective development
likely from the OK panhandle up through KS/MO/IL/IA during the
late-afternoon and evening time frame. Initial impacts will be felt
further north in the first 6hr window of the period, but the
forward propagation of the convective cluster migrating out of
IA/NE should lose some strength in the morning as LLJ weakens and
cold pools run out ahead of the main bulk of precip. Still, some
embedded heavier cores could cause issues along and north of I-80
latitude leading to a MRGL and SLGT risk maintenance over eastern
IA into northern IL.

As we move into the afternoon and evening, attention will turn to
the southwest from the initial impact areas with a broader focus
over northeast NM and points northeast through KS/northwest MO as
the next round of heavy convection takes shape. A sharp theta_E
gradient will likely denote the position of the cold front with
a long run of surface-850mb convergence located within the confines
of the front as it bisects the above areas. Surface low off the
High Plains of southeast CO will slowly move east-northeast into
the High Plains of KS by late-afternoon allowing for a maturing
south to southeast in-flow within the eastern flank of the low
which will set the stage for ample moisture pooling and
strengthening low-level convergence signature referenced above.
Convection will fire under the low's influence across southwest KS
into the adjacent OK/TX panhandles with mean cell motions
relatively weak within the low's proximity. Further to the
east, general destabilization in the warm sector will further
convective development over eastern KS into northwest MO with
increasing training potential as Corfidi vectors indicate a
weakening upshear wind profile as we move into the evening,
especially in the confines of the front.

Heavy rainfall potential is elevated due to the deep moisture
presence across the Central and Southern Plains with a strong
consensus in both deterministic and ensembles for >2" PWATs located
over central and eastern KS up into the northern half of MO. 00z
HREF neighborhood probs for >3" are between 50-80% over a large
portion of KS with the highest probs over northeastern KS near
Topeka and along the I-70 corridor. Probs for >5" are running
between 20-35% for the same areas. Areal average of 2-3" is fairly
pronounced within the means, but the key is some of the deterministic
from CAMs, and even some of the globals are indicative for local
maxima between 4-7" with even a few 8+" thrown in for good measure.
This setup is one that could entice an upgrade in future updates
with the highest potential likely over eastern KS into northwest MO
due to wetter antecedent soils and lower FFG's compared to areas
back into southwest KS. That being said, this is one setup to keep
a close eye on as locally significant flash flood potential is
becoming more favorable as we step through the forecast cycles. If
the probs trend even more favorable, there would be merit to see a
targeted upgrade. For now, a broad SLGT risk with high end SLGT
embedded over eastern KS into MO.

...Central and Southern Rockies...

Isolated to widely scattered convection will initiate, once again
across the Front Range back into the Central and Southern Rockies
with localized maxima likely contributing to scattered flash flood
prospects in their wake. The primary ascent pertains to the
diffluent area ahead of the closed reflection over CA through the
forecast period. Enough of a deep moisture presence and modest
instability up through the Continental Divide and points east will
be suitable for another day of convection with the best opportunity
for flash flooding likely located in proximity of the complex
topography centered over northern NM through CO and southeast WY.
HREF probs indicate a general 1-3" type maxima in any cells that
develop which would bring a threat for local flash flood concerns,
similar to the past few days. The good news for today is the deeper
moisture presence will be less pronounced, so seeing a downward
trend in the potential overall. In any case, still enough for one
more day of impacts lead to MRGL risk continuity from previous forecast.

...Southeast...

The presence of a slow-moving surface reflection and eastward
progressing upper trough across the northern Gulf will lead to
another period of heavy rainfall within the confines of the
Southeast CONUS. Greatest opportunity will lie along the central
Gulf coast where the proximity of the surface low and attendant
surface trough could allow for short periods of convergence in-of
areas along and south of I-10 from LA back into the FL panhandle.
Guidance remains inconsistent on any organized convective placement
with a smattering of heavy QPF bullseyes anywhere along the Gulf
coast with even some extending back up through the GA and portions
of the Carolina's. With PWATs remaining up inside the 90-99th
percentile along the immediate coast and suitable instability
presence, the previous MRGL was maintained with general continuity.

...Northern California and Adjacent Areas...

A narrow tongue of elevated moisture on the northern periphery of a
closed upper reflection along the CA coast will lead to a period of
convective development within the northern Sierra's through
northern CA and southern OR. PWATs running ~1 standard deviation
above normal and MUCAPE between 500-1000 J/kg should be sufficient
for scattered convective initiation along the ridges which could
easily produce local 0.5-1+" of precip in a short time. Given the
favorable pattern into the terrain still dealing with remnant burn
scars and complex drainage, the risk for at least isolated flash
flooding still has merit. The previous MRGL risk was generally
maintained with only minor adjustments.

Kleebauer
$$
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FOUS30 KWBC 311953
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
353 PM EDT Thu Jul 31 2025

Day 1
Valid 16Z Thu Jul 31 2025 - 12Z Fri Aug 01 2025

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE NORTHERN MID-ATLANTIC...

...Mid-Atlantic into New England...

16Z Update...

Forecast remains on track for numerous instances of flash flooding
to impact parts of the Mid-Atlantic, including the I-95 corridor
between northern VA and southern CT, some of which could be
significant and occur during the afternoon/evening commute. The
Moderate Risk was expanded in the 16Z update to include the
remainder of southern NJ and more of central DE after evaluating
12z CAMs. A >120kt jet streak located across southeast Canada
places the Northeast and Mid- Atlantic within the favorable right-
entrance region of the upper jet, while a stationary front at the
surface was analyzed this morning to stretch from coastal southern
New England through southern PA. With forcing in place to trigger
thunderstorm development, moisture and instability are also
sufficient. SPC's mesoanalysis highlights PWs widely over 1.7" and
over 2.0" into northern VA and central MD. This equates to near the
90th climatological percentile. Potentially even more impressive
is the available instability this morning. SBCAPE values have risen
above 4,000 J/kg throughout northern VA, central MD, and into
southeast PA and with southerly 850mb flow feeding this instability
even further. A very tight gradient exists along the front with
very low instability north of the Lower Hudson Bay and southern New
England. However, this tight instability gradient may also be the
focus for repeating cells capable of containing torrential
rainfall given the mean layer flow parallel to this gradient and
out of the west- southwest at 20-30kts.

After initial convection that has already developed as of 1530Z
this morning across eastern PA into northeast MD, the expectation
is backbuilding should occur in a west-southwest to east-northeast
orientation and continue through the evening as better upper
forcing and associated surface low will sweep through tonight.
This could lead to some areas within the MDT falling between maxes
and not seeing much rain at all, but areas within these heavier
axes could see localized totals up to 5-8". 12z HREF neighborhood
probabilities for >3" in 6 hours are very high and widely above 50%
between central/southern MD and NJ. Overall, the highest HREF
signal for greater than 5" totals exist across central NJ and near
parts of MD near the Chesapeake Bay. Additionally, 1 hour
probabilities for >2" are also impressive and with scattered values
between 40-60%, highlighting the rainfall rates associated with
efficient rainfall producing thunderstorms. Should these rainfall
rates (2-3"/hr) occur over urbanized locations, the large
concentration of pavement and impervious surfaces will likely lead
to extremely rapid runoff and potentially significant flash
flooding. Even outside of the major urban centers, these rainfall
amounts could lead to widespread instances of flash flooding through tonight.

Snell

Previous Discussion...

A potent vorticity max paralleled with an exceptionally strong
upper level jet streak over southeast Canada and highly anomalous
moisture content will spin up a surface low along a frontal
boundary over the northern Mid- Atlantic and spread enhanced
rainfall to a vast portion of the East. There are two areas of
concern regarding heavy rainfall. The first area is from northeast
Pennsylvania on east through the Lower Hudson Valley and into
southern New England will have a band of heavy and efficient
rainfall. PWATs will rise to the 1.8-2.0" range and low-level WAA
ahead of the front will give rise to potential training. There is
uncertainty regarding the amount of available instability, which
could reach as high as 500 J/kg. Still, the modeled soundings
depict warm cloud layers up to 13,000ft deep, so while rates may
not be as high as farther to the south, warm rain processes could
still provide 1-1.5"/hr rates in these areas Thursday afternoon and
into Thursday night. A Slight Risk remains is in place for these
regions with locally significant flash flooding possible,
particularly for areas closer to the Poconos, higher elevations of
southern New England.

Farther south, while the Mid-Atlantic region is a little farther
removed from the jet-streak dynamics to the north, the region is
closer to the deepening surface low with strong surface-925mb
southerly theta-e advection directed into the surface front. From
northern NJ and southern PA on south to northern VA, a tropical
air-mass (depicted by 2-2.25" PWATs and mid 70s dew points) will
coincide within a warm sector that becomes increasingly unstable
(MUCAPE between 1,000-2,000 J/kg). It is worth noting that SST
anomalies along the Mid-Atlantic and Southeast coasts are well
above normal too, acting as an abnormally rich moisture source for
southerly low-level flow to draw from. By this afternoon, low-
level WAA into the front will support storms enveloping the region
with additional storms from the Appalachians tracking east. Modest
vertical wind shear aloft will also support organized clusters of
storms, some of which will have the potential to backbuild and
train over the I-95 corridor into Thursday night. Latest 12Z HREF
guidance shows 24-hr probabilities for >3" of rainfall are high

70%) from the DC/Baltimore area on north through northeast MD,

southeast PA, and into southern NJ. Just as concerning is this same
region sports 30-60% chances for >5" of rainfall.

Impact potential for Moderate Risk Area: These probabilities
listed above serve as signals in ensemble guidance that highlight
the potential for significant flash flooding throughout the country,
let alone over a highly populated urban corridor. Given the
atmospheric parameters in place, it is possible that the Mid-
Atlantic I-95 corridor witnesses thunderstorms that produce
rainfall rates up to 3"/hr, with perhaps the most intense storms
potentially generating 2" rainfall totals in as little as 30
minutes. QPF may seem light at first glance given the hourly
rainfall rate potential, but this is largely due to lingering
uncertainty in the placement of the heaviest rainfall. Many
individual convective models show localized totals surpassing 5"
with even some localized maxima approaching 8". Residents in the
Mid-Atlantic should ensure they have reliable means of receiving
warnings issued by their local WFOs throughout the day and into Thursday night.

...Gulf Coast into Ohio Valley...

Slow moving thunderstorms will persist today and tonight over a
vast area south of the cold front. High PWs and CAPE and
convective coverage will drive a localized flash flood risk. A
lack of organization may keep FFG exceedance coverage down, but
high rainfall rates will likely locally approach or exceed FFG.
This region is covered by a Marginal Risk for excessive rainfall
and isolated flash flooding.

...Rockies into the Plains...

Scattered thunderstorms expected to fire up from eastern
Arizona/New Mexico northward to Montana. In general, the storms
will likely lack organization for a more elevated threat for flash
flooding. The Marginal Risk was expanded to include more of WA/OR
up towards the eastern Cascades as an upper low lifts across the
region and intersects with PW values above the 75th climatological percentile.

Snell/Mullinax/Campbell
$$
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FOUS30 KWBC 022000
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
400 PM EDT Sat Aug 2 2025

Day 1
Valid 16Z Sat Aug 02 2025 - 12Z Sun Aug 03 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE SOUTHEAST, SOUTHERN PLAINS, AND NORTHERN PLAINS...

...Southern Appalachians through the Gulf Coast...
A wavering hybrid cold/stationary front will remain draped from
eastern Texas through South Carolina today, with a slow southern
translation of this feature expected into Sunday morning. This
front will waver (with the gradual southern progression) in a
region of broad troughing extending down from the Northeast, with
weak flow across the Gulf Coast leading to the slow movement.
However, the front will be entrenched within a plume of elevated
tropical PWs (measured via 12Z U/A soundings of 2.2 to 2.4 inches,
nearing daily records across the area.) This will support
widespread showers and thunderstorms along the low-level
convergent boundary of the front, with generally weak west-to-east
0-6km mean winds of just 5-10 kts supporting slow storm motions,
and training thanks to this boundary parallel wind. Weak impulses
within the flow will enhance ascent leading to locally clustered
convection with rainfall rates above 2"/hr (briefly 4"/hr likely as
reflected by HRRR 15-min rainfall above 1"), and there are likely
to be two primary areas of higher excessive rain risk.

The first area is across the Southern Appalachians from northern
Georgia through eastern TN and far southwest NC. Here, a narrow
ribbon of instability 750-1000 J/kg (MUCAPE) will extend northward
and interact with increasing moist upslope flow as 925-850mb winds
veer more E/SE late this aftn into the evening. Although PW
anomalies are somewhat lower here compared to points south,
increased bulk shear and weak mean winds will support heavy
rainfall rates of 2-3"/hr within what could be nearly stationary
cells at times. 0-10cm soils in this region are saturated above
the 95th percentile according to NASA SPoRT, leading to compromised
FFG and a 60-80% chance of exceedance from the HREF.

Farther south from eastern AL though GA and onto the SC coast,
training of cells which develop along the front and within the
greatest plume of PW will support an increased excessive rainfall
risk, especially through peak heating. Although soils here are a
bit drier due to a lack of recent rainfall (7 day rainfall
generally 25-50% of normal), a 60-80% chance of 2"/hr rain rates
from the HREF and REFS could lead to stripes of rainfall exceeding
5 inches (40-70% chance from both HREF and REFS.) After
consideration of the new probabilities and 12Z CAMs, the two slight
risk areas were merged into one larger SLGT risk which encompasses
more of GA/eastern AL as signals from both the HREF and REFS were similar.

...Northern Rockies through the Southern Plains...
An elongated north-south stationary front will drape from Montana
through Texas today, while multiple mid-level impulses embedded
within generally zonal flow from the Rockies into the Plains
interact with this surface feature as they emerge from the west. At
the surface, flow downstream (east) of this stationary front will
become enhanced as return flow persists out of the Gulf, driving an
850mb LLJ to 30 kts across the Central Plains. This surging LLJ
will help draw impressive thermodynamics northward, characterized
by PWs of 1 to 1.25 inches (locally higher) overlapped with
1000-2000 J/kg MUCAPE. This will support widespread convection
developing beneath any of these shortwaves, with development most
likely along and just east of the wavering stationary front into
the more impressive thermodynamics.

Although convection is expected to move briskly eastward within any
clusters that develop thanks to 30-40 kts of bulk shear, rainfall
rates of 1-2"/hr are anticipated (30-50% chance from the HREF)
which could cause at least isolated excessive rainfall impacts,
especially across any urban areas or more sensitive soils with
lower FFG. The greatest risk appears to be across the TX panhandle
where an MCS may form tonight on the periphery of the greater
instability plume and then dive into the moisture beneath one of
these shortwaves, with a subtly higher training risk along its SW
quadrant, and both HREF and REFS 3"/24 hr probabilities peak above
40%, and the inherited SLGT risk was adjusted cosmetically. There
may be a secondary area of heavier rainfall across eastern SD and
into ND where some repeating or backbuilding convection may occur
later tonight as westerly flow in the vicinity of an MCV/shortwave
results in repeating development into the higher instability west,
and convection moves into some more sensitive soils in eastern SD
tonight. This has prompted a targeted SLGT risk for tonight as
well, which is supported somewhat by the CSU UFVS first guess field
which has a SLGT risk in the same general area, although displaced
from the HREF/REFS probabilities which drove this new excessive area.

Weiss



$$
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FOUS30 KWBC 090755
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
355 AM EDT Sat Aug 9 2025

Day 1 Valid 12Z Sat Aug 09 2025 - 12Z Sun Aug 10 2025

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FROM FAR NORTHERN
MISSOURI THROUGH MUCH OF EASTERN IOWA AND INTO SOUTHWESTERN WISCONSIN...

...Upper Midwest...
The synoptic setup for heavy rainfall is becoming increasingly
favorable as a near-textbook Maddox Frontal Pattern develops across
the Upper Midwest. This will likely result in numerous instances
of flash flooding from northern Missouri through southern Wisconsin.

The period begins with a closed 500mb low moving across southern Manitoba/Saskatchewan, which will drive an elongated trough
southeast into the Central Plains and Upper Midwest with
accompanying height falls. Embedded shortwaves shedding around the
primary closed low will help keep the trough axis aligned SW to NE
from the Four Corners into the Upper Midwest, and this is a
critical piece to the evolving setup. As the trough lingers back to
the west, the parent upper jet streak rotating into central Canada
will maintain a tail back into the Central Plains, leaving
favorable RRQ diffluence atop the region, and aligned with the
greatest height falls. Since the trough will move little during
this time, this pronounced synoptic support will be quasi-
stationary, resulting in prolonged lift across the region.

At the surface, a cold front will try to push east, but become
generally stationary from MN to KS as the upper trough lingers to
the west. This will enable a plume of elevated moisture to
continually surge northeast ahead of the front, as PWs of 2 to 2.2
inches (above the 97th percentile according to NAEFS) get drawn
northward on 850mb inflow of 20-30 kts, pushing an impressive theta-
e ridge axis northward into IA. This anomalous moisture will
combine with MUCAPE of 2000 J/kg or more to supply extreme
thermodynamics into the region, supporting heavy rainfall rates for
which both the HREF and REFS indicates has a 30-40% chance of
exceeding 2"/hr, and the HRRR (as far out as it goes) suggesting as
much as 1"/15min (4"/hr rates) at times.

The concern for Saturday, especially within the inherited MDT risk
area, then, is that multiple rounds of convection are likely as weak
impulses track aloft and 850-300mb winds remain parallel to the
front. At the same time, Corfidi vectors become increasingly aligned anti-parallel to this mean wind, indicating a high potential for
backbuilding and training, which will support total rainfall above
5" (40-60% chance), with locally as much as 8" possible (10-15%
chance). However, there is still considerable uncertainty into the
exact placement as rounds of convection, especially through any
clusters/MCS, drive the effective boundary (merged outflow with
front) north and south at times. This could result in a slow
southern push of the heaviest rainfall through the day, although
the northward advance of the theta-e ridge at times should again
push heavy rain northward as well. With a lot of spread in place,
the HREF EAS probabilities (which are extremely significant for
2"/24hrs at above 35%) were used to help tailor the MDT risk area,
which aligns quite well with the latest ECMWF EFI above 0.7.

Despite the uncertainty in exact placement, the MDT risk remains
needed for the likelihood of training/repeating intense rainfall
rates of 1-3+"/hr leading to FFG exceedance probabilities that
peak above 40%. The MDT risk was expanded slightly to the SW to
account for the latest high res CAMs as well, and numerous
instances of flash flooding are likely.

...Southeast...
Another active day of showers and thunderstorms is expected across
Florida and the coastal Southeast. The driving factor for this
widespread convection will be a trough of low pressure centered
over the eastern Gulf, with a secondary surface stationary front
draped along the Panhandle of FL to off the SC/GA coast. This
results in generally weak flow within a col in the vicinity of a
mid-level ridge, with modest onshore flow from the Atlantic
becoming subtly accelerated by the trough over the Gulf.
Additionally, weak impulses rotating around the Gulf trough will
push W/NW through the period, providing locally enhanced ascent
across the area.

Although ascent will be generally modest outside of any impulses or
sea breeze/frontal convergence boundaries, the environment will be
favorable for periods of heavy rainfall. PWs above 2.25 inches, or
above the 90th percentile according to NAEFS, will encompass the
region, and overlap with MUCAPE of 1000-2000 J/kg to support robust thermodynamics for heavy rainfall. Any ascent working into this
environment will support convection with rainfall rates of 2-3"/hr.
Cells that develop will likely move very slowly W/NW on 0-6km mean
winds of just 5-10 kts, and as propagation vectors become
increasingly aligned back into the higher moisture and anti-
parallel to the mean wind, backbuilding and repeating cells will
become likely. This could be enhanced by regeneration along sea
breeze boundaries or storm mergers, lengthening the duration of
these heavy rain rates.

Although identifying where the heaviest rainfall will occur today is challenging due to the weakly forced environment and slow-moving
storms, the HREF neighborhood probabilities support generally two
areas of heavier rainfall. The first is along the Gulf Coast of the
FL Peninsula where the W/NW inflow may allow for a more focused
region of heavy rainfall as the sea breeze becomes pinned and cells
moving westward merge with it. The other region is along the SC/GA
coasts where a weak impulse moving onshore within modest WAA will
help deepen warm cloud depths and focus heavier rainfall along the
frictional land/sea convergence boundary. In both of these areas,
HREF probabilities for 5"/24hrs peak above 50%, and this could occur
atop primed soils from heavy rainfall on Friday. After coordination
with ILM/CHS/JAX, a targeted SLGT risk has been added for the
coastal plain of GA/SC where the HREF signal is most impressive and
rounds of storms effectively converging along the coast could
produce repeating rounds of heavy rainfall.

...Southwest...
A mid-level ridge centered across southern NM will gradually
weaken today in response to an impressive trough amplifying across
the Northern Rockies and a weak mid-level impulse rotating westward
from Texas beneath it. This feature is progged to track along the
international border before gradually rotating northwest late in
the period, and locally enhanced ascent in the vicinity of this
impulse will drive renewed and focused convection. As this
shortwave tracks W/NW, it will impinge into a narrow corridor of
elevated PWs above 1.25 inches aligned with a similar narrow
channel of MUCAPE above 1000 J/kg. Together, this will provide an
environment that will support thunderstorms with heavy rainfall as
reflected by simulated reflectivity from the available CAMs
including the HRRR-forced and GFS-forced UA WRF.

Storm motions beneath this weakening ridge will be quite weak and
variable, as expected, with 0-6km mean wind vectors showing a
variety of directions and speeds of just 5-10 kts. With bulk shear
remaining minimal, this indicates that pulse-type storms with
generally limited lifespans will be the primary storm mode, and in
the weakly forced environment this will allow for outflows and storm
mergers to result in additional, and at times more intense,
redevelopment. Rainfall rates could exceed 1"/hr at times (20-40%
chance) which through mergers and slow motions could produce 1-2" of
rain with locally higher amounts. Briefly considered a small SLGT
risk over the area of greatest instability near Tucson, but wide
variation in coverage among the various CAMs combined with recent
dryness across the area precluded the confidence for an upgrade at this time.

...Central High Plains...
The tail end of a front stretching from the Upper Midwest will
linger across the Central High Plains today. As a trough upstream
deepens over the Northern Rockies and sheds spokes of vorticity
eastward, these will interact with the lingering front to produce
scattered showers and thunderstorms late this afternoon through
tonight. Impressive bulk shear of 35-50 kts combining with moist
E/NE 850mb flow will result in slow moving thunderstorms organizing
into clusters, with repeated development likely upstream. Coverage
of storms may be isolated to scattered according to high-res CAMs,
but the slow motion of any cell that develops combined with
anticipated rain rates above 1"/hr may produce isolated flash flooding.

Weiss
$$
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FOUS30 KWBC 100835
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
435 AM EDT Sun Aug 10 2025

Day 1 Valid 12Z Sun Aug 10 2025 - 12Z Mon Aug 11 2025

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
KANSAS AND MISSOURI...

...Central Plains through the Upper Midwest...
The synoptic pattern today continues to be indicative of a Maddox
Frontal rainfall event, although confidence in the exact evolution
has decreased and significant changes are needed to the inherited
ERO. Some of these changes are due to exceptional model uncertainty
at this time range, but also accounting for what occurred Saturday
when the event did not really pan out as expected.

Synoptically, the setup still remains extremely favorable for an
axis of very heavy rainfall. An anomalous mid-level trough (500mb
and 200mb heights locally below the 10th percentile according to
NAEFS) will remain aligned from ND/MN southwest through the Four
Corners. Although the leading impulse embedded in the core of this
trough will advect east across southern Canada, spokes of vorticity
and associated shortwaves rotating through the flow to the south
will force the trough axis to remain to the west. Downstream of this
trough axis, a persistent upper jet streak will arc poleward into
Ontario, placing at least modest but persistent upper level
diffluence within its RRQ. Beneath this evolving setup, a surface
front will oscillate at least subtly NW to SE as a stationary front,
providing additional focus for ascent beneath the weak height falls
and periods of PVA. Additionally, any stronger impulse interacting
with the surface front could result in waves of low pressure
rippling along to the northeast.

East of this front, low-level return flow will continue to advect
from an open Gulf, drawing elevated thermodynamics and theta-e
northward. PWs are progged to climb to above 2 inches as the 850mb
LLJ surges to 20-30 kts, overlapping intense MUCAPE of more than
3000 J/kg to provide an extremely favorable environment for heavy
rain, which is additionally supported by specific humidity values
between 925-850mb above the 97th percentile (NAEFS). At the same
time, the theta-e ridge will blossom and align into the front, with
an intense gradient suggesting heavy rainfall on its NW axis as is
typical with the Maddox Frontal conceptual model. In this setup,
with persistent ascent acting upon impressive thermodynamics, and
mean 0-6km winds aligned to the front, it is likely streaks of heavy
rainfall will occur, and most deterministic models showing 1-4
inches of rainfall through 12Z Monday, with high-res CAMs indicating
locally 5-7 inches, so heavy rainfall is almost a certainty.

However, uncertainty is exceptional (especially for a 24-hr
forecast) with the placement of this heavy rain, and the spread in
placement ranges from southwest WI to southern KS, and almost
anywhere in between, leading to a challenging ERO forecast.

While the front will be the primary focus for convection, along with
a wave of low pressure expected to develop along it, and the LLJ is
likely to be parallel to it, there is increasing concern that
convective clusters (both overnight Saturday night into Sunday, and additionally on Sunday) will leave outflow boundaries aligned more
west-to-east outrunning the front. This could drastically change the
position of the heaviest rain axes, and would support heavy rainfall
south of the global members in a typical bias. If these clusters do
not develop, convection and heavy rainfall would likely remain more
aligned SW to NE, but have noted a trend in the Corfidi vectors to
be more pointed S/SE after SW early, which would additionally
support more W-E heavy rainfall. With all the uncertainty in
placement, the ERO was modified heavily and tailored primarily to
HREF/REFS neighborhood probabilities, but with additional changes
influenced by the EAS probabilities, the CSU first guess fields,
and coordination with the impacted WFOs.

...Southeast...
Another active day of convection is likely from the coastal
Carolinas through Florida.

Broad ridging extending from a Bermuda-type but elongated high
pressure over the Atlantic will be modified by an inverted trough
aligned from the eastern Gulf to the NC coast. Onshore and confluent
flow into this inverted trough will maintain impressive moist
advection into the area, manifesting as PWs above 2.25 inches, well
above the 90th percentile according to the SPC sounding climatology.
This will overlap with MUCAPE of 500-1000 J/kg, modest overall
instability indicative of a tropical airmass, to produce impressive thermodynamics to support heavy rainfall. Additionally, this robust thermodynamic advection onshore will result from 850mb winds as high
as 15 kts, which, while modest, will exceed the mean 0-6km winds
which are progged to be just around 5 kts. This suggests widespread
convergent ascent across the Southeast, with the accompanying WAA
surging warm cloud depths to around 15,000 ft, supporting efficient
warm rain processes within a deeply saturated column noted in
regional forecast soundings.

The CAMs are in generally good agreement in widespread convection
today. Scattered slow-moving thunderstorms with rainfall rates of 1-
3"/hr are expected across much of FL and into GA/AL. However, the
focus for the heaviest rainfall is likely along the coastal plain of
GA through southeast NC. Here, propagation vectors are aligned
against the weak mean wind, and with subtle mid-level impulses
lifting northwest within the weakly forced environment, waves of
repeating rounds of convection with heavy rainfall are likely. In
this region, the HREF indicates a 20-30% chance of 2"/hr rain rates,
with locally more than 3"/hr possible at times, at least briefly.
With backbuilding offshore leading to regenerating and training
rounds of heavy rain, total rainfall could exceed 5" (30-50% chance
from the REFS/HREF), with the greatest potential along the SC coast.
The inherited SLGT risk was cosmetically adjusted, but scattered
instances of flash flooding appear likely today, even across these
areas that are generally more difficult to flood.

...Southwest...
A MRGL risk of excessive rainfall continues for portions of the
Southwest today as monsoonal moisture returns to the area leading
to a more active convective pattern. A mid-level trough extending
down from the Northern High Plains will deepen today, producing
lowered heights across the Four Corners and Desert Southwest,
through which weak spokes of vorticity will rotate. These lowered
heights and locally enhanced ascent will impinge into an
increasingly favorable thermodynamic environment to support
convection with heavy rainfall as low-to-mid level flow backs
gradually to the SW, allowing for a better draw northward of PWs
exceeding 1", which may spread as far north as the Mogollon Rim and
combine with MUCAPE of 500-1000 J/kg across the southern half of
AZ and NM. This will support scattered to widespread showers and
thunderstorms which will move slowly eastward through the day. With
rainfall rates as much as 0.75"/hr to 1"/hr at times as shown by
the UA WRF and HREF neighborhood probabilities , this could result
in at least isolated instances of flash flooding, especially across
more vulnerable soils or terrain. The MRGL risk was curtailed a
bit on the eastern side across NM where CAPE is progged to be much
weaker, but in general changes to the inherited risk were minor.

...Central High Plains...
The inherited SLGT risk was maintained across eastern CO,
primarily for renewed thunderstorm activity on Sunday evening
falling atop soils that will be primed from ongoing (Saturday
night) convection. The elongated stationary front across the
Central Plains early today will drop steadily southward, leaving NE
upslope flow in its wake. This will be most pronounced into
eastern and southeastern CO, where PWs will likely surge to above 1
inch. As convection develops across the higher terrain of CO
during the aftn, it should steadily progress east and then grow
upscale as it moves off the terrain in response to bulk shear of 40
kts. While these clusters should move steadily eastward on mean
0-6km winds of 15-20 kts, rainfall rates of 1-2"/hr are likely
which could be sufficient to overwhelm soils that will be saturated
from antecedent rainfall. Additionally, some local backbuilding is
possible as reflected by CAMs across southeast CO, lengthening the
potential duration of heavy rainfall in a few areas.

Weiss
$$
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FOUS30 KWBC 140754
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
354 AM EDT Thu Aug 14 2025

Day 1 Valid 12Z Thu Aug 14 2025 - 12Z Fri Aug 15 2025

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

...Southern New England through the Lower Mississippi Valley...
Surface cold front draped from New England through the Ozarks will
drift gradually southeast but generally stall across the region
Thursday as the parent trough begins to fill, leaving gradually
more zonal flow over the eastern CONUS. Although heights will
gradually rise, weak shortwave impulses embedded within the flow
will maintain periodic ascent atop the front to create waves of low
pressure rippling northeast to produce locally enhanced lift, and
scattered to numerous thunderstorms are again expected across the
east on Thursday, primarily from southern New England through the Gulf Coast.

Thunderstorms that develop will all have the potential to produce
pockets of heavy rainfall as thermodynamics remain impressive. PWs
of more than 2 inches will remain in a plume arcing within return
flow around offshore high pressure from the Florida Panhandle
through the northern Mid-Atlantic states. This PW will overlap with
elevated MUCAPE of 1000-2000 J/kg to create the favorable
thermodynamics for heavy rainfall, and the HREF indicates scattered neighborhood probabilities for 2"/hr rain rates across much of the
area supporting the broad inherited MRGL risk.

However, there appears to be at least a signal for some more
organized convection with a greater threat for excessive rainfall
across the eastern Carolinas and into Southeast Virginia. This
region will benefit from additionally focused ascent through the
presence of the cold front and a surface trough, upon which a more
pronounced shortwave is progged by the consensus of the models to
lift northeast during peak heating. This will promote at least
modest bulk shear to support multi-cell clusters across this area,
while most of the rest of the east should generally feature pulse
type thunderstorms. Additionally, mean 0-6km winds and propagation
vectors are aligned and parallel to the boundaries, suggesting an
enhanced training risk as well, which additionally supports the
elevated HREF and REFS probabilities for 3"/24hrs (and lower but
still notable 5"/24 hrs). For this reason the inherited SLGT risk
was adjusted to spread farther south into the eastern Carolinas.

...Southwest...
Mid-level ridge centered over NM to start Thursday morning will
weaken in response to height falls approaching from CA as a trough
digs down the Pacific coast. This will have the two- pronged affect
of lowering heights across the Desert Southwest/Four Corners
region, while also leading to increased cyclonic flow emerging
from near Baja to push a potent shortwave northward across AZ and
into UT. Additionally, this increasingly south flow, especially
between 850-700mb, will transport elevated PWs northward, and a
plume above 1" is progged to surge almost to UT by the end of the
forecast period. Where this combines with MUCAPE above 500 J/kg,
slow moving storms (0-6km mean winds of just around 5 kts to the
north) could become more organized leading to a longer duration of
heavy rainfall rates of 0.5-1"/hr. The total coverage is still
somewhat uncertain so the inherited MRGL risk still appears
appropriate, but this was expanded north to match recent guidance,
and convection is likely to be more widespread Thursday than it was
on Wednesday.

..Upper Mississippi Valley...
A warm front will lift northeast towards Minnesota today,
accompanied by a surge of 850mb winds to 20-30 kts advecting
anomalous PWs of 1.5 to 1.75 inches northeastward (+1 to +1.5
standard deviations above the climo mean). This front will be
driven eastward by a potent but flat and fast- moving shortwave
embedded within the nearly zonal flow aloft, leading to a period
of enhanced ascent aided by the warm front and accompanying
isentropic lift of the 850mb wind. This will result in scattered
thunderstorms across the area, with bulk shear of 25-35 kts
potentially supporting some organization into clusters. The
guidance is highly variable in both the placement and intensity of
convection today, and the QPF footprint and ensemble probabilities
suffer as a result. Still, with the impressive thermodynamics in
place, thunderstorms that develop could support rainfall rates of
1-2"/hr with at least short-term training possible, and the
inherited MRGL risk was curtailed for latest guidance but continued.

...Pacific Northwest...
A rare August atmospheric river (AR) is progged to make landfall
this evening north of 45N into WA state with IVT above 500 kg/m/s
as reflected by both GEFS and ECENS probabilities above 90%. A weak
shortwave embedded within otherwise zonal flow aloft will help
produce ascent into this plume of IVT, but instability will be
negligible and jet level ascent appears to be displaced north of
the core of the AR. While deterministic model QPF output and
accompanying ensembles support a threat for heavy rainfall,
especially in the Olympics, this will be occurring atop extremely
dry soils and should generally be beneficial rainfall.
Additionally, in the AR/ERO verification data set since 2019, there
has never been an impactful (MRGL risk or higher) AR in the month
of August. For this reason, despite some heavy rain spreading
onshore this evening, no excessive rainfall impacts are expected.

Weiss
$$
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