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Excessive Rainfall Discussion...UPDATED
NWS Weather Prediction Center College Park MD
435 AM EDT Sun Aug 24 2025

Day 1
Valid 12Z Sun Aug 24 2025 - 12Z Mon Aug 25 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER THE SIERRA,
SOUTHERN UTAH, AND THE WESTERN HIGH PLAINS...

...Intermountain West to the Central Plains...

With the finer scale models maintaining and even bolstering their
signal for enhanced rainfall amounts for the Sierra Nevada range eastward/northeastward...maintained the Slight Risk area with few modifications. In places...this rainfall will be in addition to
some noteworthy rainfall amounts that fell on Saturday. With such
anomalous moisture being pulled northwestward around the upper
high/ridge axis...the expectation is that sufficiently high
rainfall rates are possible that excessive rainfall is a concern
across more the the intermountain region today compared with
Saturday.

Father east, the risk of excessive rainfall starts to spread out
away from the Front Range of the central Rockies, and out over the
adjacent Plains in a region of low level southerly flow drawing
moisture northward while a broad area of surface high pressure at
the surface and fast northwest flow aloft pushes a cold front south
into parts of the central plains. This should set the stage for an
MCS later tonight across parts of Colorado that spreads eastward
and southward. The latest runs of the RRFS has been favoring
heavier rain in southwest Kansas and portions of the Oklahoma and
Texas panhandles...while the HREF has thrown in more with the
coarser/global models in heavy to potentially excessive rainfall
being confined to western Kansas. With the instability fields in
the NAM and RRFS depicting 1000 to 2000 J per kg in better upslope
flow closer to the Colorado state line...expanded the Slight Risk
area southward and westward a bit. The presence/persistence of any
low cloud cover that forms in the upslope flow will limit the
surface heating and shift the focus for storms capable of producing
heavy rainfall.

...Northern Mid-Atlantic and Pennsylvania/New York...

A strong upper trough making its way eastward from the Ohio Valley
and eastern Great Lakes should make it into Pennsylvania and New
York state before slowing. The airmass its moving into will have
500 to 1000 J/kg of MLCAPE and precipitable water values generally
in the 1.5 to 1.75 inch. With only modest low/mid level lapse
rates...a few of any storms that form could produce locally heavy
rainfall that results in localized flooding this afternoon or early
evening before convection wanes with the loss of daytime heating.

...Coastal Carolinas...

A weak surface feature in the vicinity of the coastline will focus
and support locally heavy rainfall near the coastal portions of
the Carolinas into tonight. Present indications are that the
activity should remain off-shore. However...on-shore flow and the
proximity of showers associated with the feature will keep the risk
of some brief heavy rainfall along the immediate coast today. Any
risk of excessive rainfall should taper off from south to north as
the system continues to move northeast.

...Southern Georgia and northern Florida...

On-shore flow of moist air interacting with the southern end of the
front associated with the low pressure/amplifying upper trough to
the north should combine to focus/support convection capable of
producing heavy rainfall Monday and Monday evening across portions
of southern Georgia into the northern Florida peninsula.

Bann

Day 2
Valid 12Z Mon Aug 25 2025 - 12Z Tue Aug 26 2025

...THERE ARE SLIGHT RISK OF EXCESSIVE RAINFALL AREAS OVER
PORTIONS OF THE CENTRAL ROCKIES FRONT RANGE AND THE SOUTHERN
PLAINS ON MONDAY...

Broad cyclonic flow aloft will be in place across the Plains on
Monday while south to southeasterly low level flow continues to be
drawn northward at low levels across the Southern Plains, with a
boundary extending from northern Texas into northeast New Mexico
and southern Colorado helping to focus another round of late day
storms once an MCS weakens and dissipates in the morning. The
airmass south of the front is expected to have PWs approaching 2
inches across the region and values potentially in the 2 to 2.25
inch range near the Red River. The overnight numerical guidance
still supports the idea of two distinct regions of rainfall and saw
little reason to make more than minor adjustments to the two Slight
Risk areas from the previous outlook. Instability does not appear
impressive at this point, but the atmosphere should support locally
heavy rainfall should convection develop anywhere between
Oklahoma/northern Texas westward into the plains of eastern
Colorado and northeast New Mexico.

The Slight Risk areas were embedded within a broader Marginal Risk
area extending across much of the central and southern portion of
the Great Basin and eastward to the central and southern Rockies
Front Range. Once again...weak shortwave energy embedded within a
broad upper leads to yet another round of late day showers and
thunderstorms. Slot canyons...normally dry washes and burn scars
remain most at risk for flooding.

Bann

Day 3
Valid 12Z Tue Aug 26 2025 - 12Z Wed Aug 27 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE CENTRAL AND SOUTHERN ROCKIES AS WELL AS ADJACENT PLAINS...

With a sprawling upper ridge in place...the potential exists for
excessive rainfall will exist as anomalously deep moisture
provides an environment supportive of brief but locally intense
rainfall rates from any daytime or evening storms that form. The
numerical guidance showed a more coherent signal for organized
heavy rainfall from southern Colorado into northern New Mexico
where low level flow is transporting moisture upslope and
instability peaks at around 1000 J per kg in the late day with shortwave
energy moving north-/northeastward across western New Mexico.

Bann

Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!_1KEWPedNJElK0yGbktjDh76P5UogD0LQQCbfpqfSj8p= u6_MmSQeoOxMavchpkPDAiSgvryNg0ljhG8kCFB4V2oC_XQ$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_1KEWPedNJElK0yGbktjDh76P5UogD0LQQCbfpqfSj8p= u6_MmSQeoOxMavchpkPDAiSgvryNg0ljhG8kCFB4am4xNkY$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_1KEWPedNJElK0yGbktjDh76P5UogD0LQQCbfpqfSj8p= u6_MmSQeoOxMavchpkPDAiSgvryNg0ljhG8kCFB4TsaXWdA$=20

=3D =3D =3D
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