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Excessive Rainfall Discussion...UPDATED
NWS Weather Prediction Center College Park MD
453 AM EDT Fri Jul 25 2025

Day 1
Valid 12Z Fri Jul 25 2025 - 12Z Sat Jul 26 2025

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE CENTRAL PLAINS, MIDWEST, AND OHIO VALLEY...

...Central Plains to southern Great Lakes...

Deep moisture and a front extending from the Plains to New England
is the main focus for potentially excessive rainfall today and
tonight...especially across the plains where surface low pressure
helps focus convection along the front.  However...plenty of
uncertainty lingers with the evolution/progression of the low...any
MCV or outflow boundary that could disrupt placement/magnitude of
any forcing in the low levels...and a mid- and upper- level
disturbance hugging the Gulf coast. Despite that uncertainty...and
in deference to the convective evolution Thursday night/early
Friday morning prior to the start of the Day 1 period combined with
the amounts still expected to fall being in largely the same
geographic placement...warrantied a the upgrade to a Moderate risk
in the Plains. Local 1.5 to 3 inch per hour rainfall rates and 2
to 4 inch rainfall totals along with isolated higher maximum
amounts remain in the realm of possibilities. A Slight risk area
extended into portions of the Ohio Valley along the best moisture
transport vectors.

Downstream from there...across portions of the Great Lakes into New
England...maintained a Marginal Risk area along a corridor of 2
inch precipitable water values which should be aligned along and
ahead of the cold front. The front should continue to provide a
focus for showers and thunderstorms. Even though it is an
environment which supports isolated convection capable of
producing torrential downpours...the coverage of storms should be
much less than areas upstream and the progressive nature of
individual storms should be enough to mitigate concerns over a
widespread area.

...Northern Plains...

A quick moving shortwave ejecting out of the Rockies will sweep
across the Northern Plains later tonight/early Saturday morning
with scattered thunderstorms likely to roll through the Dakotas
after sunset. With precipitable water values climbing upwards of
+2 deviations along with ample mid-level forcing...a period of
enhanced heavy rainfall prospects during the time frame of impact.
Deterministic output remains chaotic in terms of placement and
generally low in magnitude...but 1-3" of rainfall in a short
period of time would be sufficient for at least low-end MRGL.

...Gulf Coast...

The disturbance across the northern Gulf will continue to slowly
propagate west- southwestward with an attendant surface low
remaining situated just south of the west-central Gulf coast.
Current model guidance still keeps the feature far enough offshore
to preclude widespread impacts. However, the airmass surrounding
the disturbance will still be pretty robust with precipitable water
values remaining very high (>2.3" for much of the immediate
coastal plain over TX back through the central Gulf coast.

Bann


Day 2
Valid 12Z Sat Jul 26 2025 - 12Z Sun Jul 27 2025

...THERE ARE MARGINAL RISK AREAS FOR EXCESSIVE RAINFALL OVER
MULTIPLE REGIONS OF THE COUNTRY ON SATURDAY...

...Gulf Coast...

The upper trough and associated surface low hugging the Gulf coast will
remain situated across the western half of the Gulf with the main
area of surface reflection likely coming ashore into TX during the
period. Model solutions remain varied...but high precipitable
water and enough mid- and upper level forcing to continue producing
downpours across the central and western Gulf coast with an
emphasis on the immediate coastal plain.

...Northern Plains...

The next in a series of potent shortwave will eject northeast out
of the northern High Plains resulting in another round of heavy
precip potential with more organized convective clusters migrating
through the Dakotas. Isolated 2 to 3 inch rainfall maxima are
possible and embedded within broader areas of lesser rainfall
amounts. The pattern is fairly progressive so see little reason to
move from the Marginal risk category.

...Northeastern California and Northwest Nevada...

Almost a carbon copy of the prior period for convective impacts
lingering across the Northern Sierra up through northeastern CA and
northwest OR. The upper pattern is pretty slow to breakdown with
the diffluent area in the longwave setup still situated over
northern CA into NV. Instability is expected to be modest and
slightly above normal moisture in the terrain will offer the
capability for some isolated flash flood concerns within any
complex terrain and burn scar remnants in the above area.

Bann


Day 3
Valid 12Z Sun Jul 27 2025 - 12Z Mon Jul 28 2025

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

...The eastern Dakotas to northern Minnesota... Effects of a
shortwave trough interacting with a surface front across the Upper
Midwest will continue into Sunday as does uncertainty with
placement and timing of any convection capable of supporting heavy
rainfall. There are some signals in the GFS and ECMWF for possible
MCS development while the NAM does generate some storms but would
be less concerning, Given the amount of rainfall recently across
parts of northern Minnesota...will maintain the Slight risk in
deference by the GFS/ECMWF for the time being.

...The Mid Atlantic to southern New England...
Mid-level flow flattens over the Great Lakes and Ohio
Valley...allowing embedded shortwave energy to start digging east
of there with corresponding height falls. The atmosphere will still
be anomalously moist and capable of supporting convection with
localized downpours that produce localized flooding.

...Southwest US...
Deeper moisture that made its way across parts of the Gulf and
inland across Mexico should start to be drawn northwest into parts
of the Southwest United States...resulting in scattered late day
and evening convection across parts of New Mexico and a small
portion of Arizona.

Bann
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