893
FOUS30 KWBC 242051
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
451 PM EDT Sun Aug 24 2025

Day 1
Valid 2042Z 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...

16Z update...The latest CAMs show hourly rainfall rates nearing
1-1.5 inches/hour over the higher terrain of central Colorado and
upwards of 2.5 inches/hour associated with the MCS as cells move
across far northeast portions of the Texas Panhandle and western
Oklahoma. The Slight Risk was expanded a bit to reflect this trend
while also edging westward into central Colorado and northward
into southwest Nebraska.

Campbell

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.

Farther 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...

2018Z Update...Expanded the Marginal Risk area a little farther
southward (into parts of central MD, far eastern WV, and western
VA) based on the latest observational trends and mesoanalysis,
along with the recent updates of the HREF (18Z) and RRFS (12Z)
rainfall exceedance probabilities for the rest of this afternoon
through late this evening (through ~03Z).

Hurley


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...

16Z update... With the convection mostly offshore the threat for
excessive rainfall has diminished therefore the Marginal and Slight
Risk areas along the coastline were removed.

Campbell

...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 FOR SOUTHERN
ARIZONA AND OVER PORTIONS OF THE CENTRAL ROCKIES FRONT RANGE AND
THE SOUTHERN PLAINS ON MONDAY...

21Z update... Anomalous monsoonal moisture advecting northward
into southern Arizona will help trigger enhanced rainfall that may
increase the threat for flash flooding. In coordination with the
local forecast offices, a Slight Risk area was raised for this
increased threat. The latest guidance continue to focus scattered
convection over the higher terrain and surrounding areas of
central Colorado and northern New Mexico. A increase across north-
central new Mexico was noted therefore the Slight Risk was expanded
westward to cover this area. Meanwhile, guidance depicted a small
eastward shift of the QPF footprint across the Plains. In turn, the
Slight Risk area was adjusted to cover more of central Arkansas.

Campbell

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...

21Z update... The increased influx of monsoonal moisture will
persist, yet shifting to the east and adjusting where the enhanced
rainfall potential will setup. A Slight was raised for portions of
southeast Arizona for this period. The latest guidance and WPC QPF
depicted a small northwest shift of the higher QPF footprint over
Colorado and New Mexico and so the Slight Risk area was altered
accordingly. The Marginal Risk was reduced some from north-central
Texas and increase across southern Kansas and central Oklahoma.

Campbell


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://www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Day 2 threat area: https://www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Day 3 threat area: https://www.wpc.ncep.noaa.gov/qpf/99epoints.txt