FOUS30 KWBC 311953
QPFERD

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

Day 2
Valid 12Z Fri Aug 01 2025 - 12Z Sat Aug 02 2025

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

...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 Friday and 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%.

Only minor adjustment to the previous outlook was to reduce the
northern portion of the SLGT and MRGL based on southern trends in
the progression of the cold front. 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...

The cold/stationary front continues to stretch westward towards the
southern Plains along with PW values near 2" Friday into Friday
night. While most activity should remain pulse-like, a surface wave
and meandering MCV could trigger locally heavy rain in
northern/northeast TX Friday night. The location remains somewhat 
uncertain, but this area is highlighted by the 12z HREF as having 
6-hr probabilities for >5" at 30-40%. Additionally, the RGEM and
ECMWF included elevated QPF values above 2-3" with the 12z runs in
a very similar location. This potential collocated with the 
Dallas- Fort Worth metro led to enough confidence for a targeted 
Slight Risk. Expect refinements in future outlooks as more CAM runs
become available and/or the MCV at play becomes more trackable.

...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 inches/hour across 
the Dakotas. There is also the potential for an MCV across the
Dakotas to provide a focus for locally intense rainfall, but the
location of this heavy rain remains too uncertain for an upgrade to
a Slight Risk. This potential will be evaluated in future outlooks.

Snell


Day 3
Valid 12Z Sat Aug 02 2025 - 12Z Sun Aug 03 2025

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

...South and Southeast...

The strong front mentioned will continue pressing southward,
draped from the Southeast westward across the Deep South, Lower
Mississippi Valley and over Texas. High moisture content and
instability along and ahead of the front interacting with the right
entrance region of the upper jet will promote heavy to excessive
rainfall in thunderstorms that could cause localized flash
flooding. Very heavy rainfall rates are expected and should drive
an isolated to scattered flash flood risk. A Slight Risk remains in
effect for portions of the Lowcountry South Carolina, southern 
Georgia and far northern/northeast Florida. 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. Location in
heaviest rainfall remains too uncertain for an upgrade to a Slight
Risk at the moment and MCS activity may bode too progressive for
widespread flash flooding, thus the region is covered by a Marginal Risk.

Snell/Campbell
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