FOUS30 KWBC 010821
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
421 AM EDT Fri Aug 1 2025

Day 1
Valid 12Z Fri Aug 01 2025 - 12Z Sat Aug 02 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE CAROLINAS, NORTH/NORTHEAST TEXAS, NORTHEAST NEW MEXICO AND THE DAKOTAS...

...Southeast and Mid-Atlantic...

During this period a potent cold front will be dropping south 
through the region in response to a very strong surface high 
pressure (above the 99.5th climatological percentile per the NAEFS)
over the Great Lakes/Midwest. This will allow for moisture to pool
along the front and thunderstorms to develop across the Carolinas 
on through Friday night. Meanwhile both terrain and coastal 
influence are also likely, which may lead to slower storm motions 
and heavier rainfall amounts. This combination will also result in 
good convective coverage, which will ultimately likely lead to a 
decent degree of cell merger activity. Much of the area will have
PW values nearing 2.5 inches along with abundant instability, 
resulting in very heavy rainfall rates over 2"/hr in this 
thermodynamic environment. Given the likelihood of cell mergers and
westerly mean layer flow nearly parallel to the front, this should
drive an isolated to scattered flash flood risk. 12z HREF guidance
depicted high neighborhood probabilities (60-90%) for at least 3" 
in 6-hrs along the coastal Carolinas, where FFG is also highest. 
Additionally, along the complex terrain of the western Carolinas 
12z HREF neighborhood probabilities for exceeding 3" in 6-hrs are 40-50%.

Urban areas and the complex terrain of the southern Appalachians 
remain most at risk to scattered instances of flash flooding, with 
the remainder of the Carolinas flat and sandy soils capable of 
soaking in most of the intense rainfall. The frontal boundary will 
also linger across the remainder of the Southeast and into the 
Lower MS Valley, where additional instances of flash flooding are 
possible given weak steering flow and 2-2.25" PWs. However, most 
storms should become outflow dominant and be short-lived after a 
brief period of intense rainfall and rates up to 3"/hr.

...Southern Plains...

During this period a cold/stationary front will be draped across
the region within a pool of PW values near 2 inches. A surface 
wave and meandering MCV could trigger locally heavy rain in 
northern/northeast Texas Friday night. The exact location of
remains somewhat uncertain for the highest QPF however hi-res
guidance indicate 6-hr probabilities for >5" at 30-40%. A Slight
Risk was maintained with some expansion northward in northeast Texas.

...Rockies and Plains...

Scattered convection is expected to span from Montana to New Mexico
into Friday. The most favorable environment for heavy rainfall will
likely setup from Montana into the Dakotas, which is where mid
level troughing will be paired with the highest PW anomalies in
the CONUS...above the 90th percentile climatological early August
peak values. Combine this with CAPE forecast around 2000 J/kg and
the environment appears conducive to areas of localized flash flooding.

Hourly rainfall rates up to 1.25-1.5 inches/hour possible
over the Northern Rockies/Montana and up to 2-2.5 inches/hour 
across the Dakotas. Although there still remains some uncertainty
on the exact location of an advancing MCV, guidance suggests
portions of south-central North Dakota and much of central South
Dakota will have an elevated threat for excessive rainfall and
isolated to scattered areas with flash flooding. A Slight Risk was
raised for this part of the Northern Plains.

Additionally, a Slight Risk was raised for northeast New Mexico
that covers parts of I-25/eastern Sangre de Cristo Mountains and
near I-40 and points to the north/northeast. Enhanced rainfall will
elevate the risk for runoff and flash flooding over the sensitive
terrain. Hourly rain rates may reach 1.5 inches/hour.

Campbell/Snell


Day 2
Valid 12Z Sat Aug 02 2025 - 12Z Sun Aug 03 2025

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

...South and Southeast...

During this period the strong cold front will sink southward
through the Southeast, Deep South and westward in to Texas. A deep
pool of moisture will remain readily available enhance local 
rainfall, especially with the presence of instability along and 
ahead of the front interacting with the right entrance region of 
the upper jet. Very heavy rainfall rates are expected and should 
drive an isolated to scattered flash flood risk. The Slight Risk 
are was maintained for portions of the Low Country South Carolina,
southern Georgia and far northern/northeast Florida and was 
expanded western into Alabama with this issuance. The front 
stretching west across the Gulf Coast states in a moist and 
unstable environment could promote scattered diurnal thunderstorms 
into Saturday thus maintaining the Marginal Risk.

...Rockies and Plains...

Shortwaves rounding the eastern edge of the upper ridge in the
western U.S. is forecast to interact with the same front that bends
back across the Great Plains, where rounds of rain and
thunderstorms are likely with possibly multiple MCSs. High rain
rates should be supported at times with the above normal moisture
and instability with some areas possibly seeing repeated rounds of
storms as the front begins to lift as a warm front. While the the
location of the heaviest accumulations remain somewhat uncertain
the guidance is favoring locations in the vicinity of western
Kansas and Oklahoma. A Slight Risk was upgraded for this portion of
the plains. 

Snell/Campbell


Day 3
Valid 12Z Sun Aug 03 2025 - 12Z Mon Aug 04 2025

...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FOR SOUTHEAST
GEORGIA AND FOR THE CENTRAL/SOUTHERN PLAINS...

...Southeast...

Once again the cold front advances further south, shifting the QPF
footprint along with it. The heaviest rainfall will likely focus
along the far southern portions of South Carolin and coastal 
Georgia, therefore kept the Slight Risk for this period. A broader 
Marginal Risk area covers the potential for isolated instances of 
excessive rainfall as far west as the Florida Panhandle and 
southeast Alabama.

...Plains...

MCSs mentioned in the Day 2 period will persist during this period
although shifted east/south further into the plains. Deep influx of
PW near 2 inches will continue to fuel convection and enhance
rainfall rates within these complexes. The exact location of the
highest totals are not certain but the higher potential for
excessive rainfall and flash flooding concerns will likely be
focused over south-central Kansas and northern Oklahoma. The Slight
Risk area was maintained for this period.

Campbell
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