FOUS30 KWBC 200821
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
421 AM EDT Sat Sep 20 2025

Day 1
Valid 12Z Sat Sep 20 2025 - 12Z Sun Sep 21 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE MIDWEST, THE SOUTHERN PLAINS, OZARKS, AND THE CENTRAL
APPALACHIANS...

...Wisconsin and northern Illinois...

A negatively-tilted upper trough will lift slowly across the mid to
upper Mississippi Valley today. The associated ascent interacting
with a ribbon of relatively deeper moisture (PWs 1.25-1.5 inches)
along a modest low level jet will support showers and storms
redeveloping this afternoon, which may potentially continue into
the evening. With differences in the details, the CAMs generally
indicate two areas of locally heavier amounts -- a north-south axis
associated with storms lifting across eastern Wisconsin during the
afternoon/evening and a west-east stripe produced by storms
developing across Iowa and then training across northern Illinois
later during the overnight. HREF neighborhood probabilities
indicate localized amounts in excess of 2 inches are possible in
these areas.

...Ozarks to southwestern Oklahoma....

CAMs indicate that ongoing convection firing north of a stationary
front over southern Kansas will continue through the late morning,
potentially producing heavy amounts as they train further east
into the Ozark Region. The HREF shows high neighborhood
probabilities for accumulations over 2 inches centered over this
region.

Then, as upstream energy sliding southeast across the central
Plains interacts with deepening moisture that will be supported by
increasing southerly low level flow, some guidance indicate that
storms will redevelop over this same area later today. However,
other models show storms developing further to the west before
moving back into areas impacted by this morning's storms.

While there is fair amount of uncertainty on how these storms
across central into eastern Oklahoma will evolve, there is greater
model consensus that storms developing over the Texas Panhandle and
western Oklahoma by this evening will merge across southwestern
Oklahoma to produce locally heavy amounts across the region during
the overnight.

...West Virginia...

CAMs continue to show isolated heavy amounts associated with slow-
moving storms that are expected to develop over eastern West
Virginia this afternoon. A weak impulse lifting northeast out of
the Ohio Valley, interacting with pooling moisture along a slowing
front, will support storm development. HREF neighborhood
probabilities indicate that amounts of 2-3 inches are likely within
the highlighted area.

Pereira


Day 2
Valid 12Z Mon Sep 22 2025 - 12Z Tue Sep 23 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE CENTRAL PLAINS, MID MISSISSIPPI VALLEY, AND THE SOUTHWEST...

...Eastern Kansas and northeastern Oklahoma to southern Illinois...

Deepening moisture (PWs above 1.5 inches) along an axis of
strengthening southerly to southwesterly flow ahead an amplifying
upper trough will fuel showers and storms, possibly producing
heavy amounts. While models differ significantly on the details,
the general consensus indicates widespread precipitation is likely,
with locally heavy amounts of 1-2 inches possible.

...Southwest...

An upper low dropping to the south along the California coast will
slow as it becomes cutoff west of Southern California. Southerly
flow ahead of the system will support increasing moisture and the
chances for precipitation across parts of Southern California and
Arizona. Both the GFS and ECMWF show PW anomalies increasing to 2.5
to 3 standard deviations above normal across far Southern
California through the lower Colorado Basin into Arizona.

Pereira


Day 3
Valid 12Z Mon Sep 22 2025 - 12Z Tue Sep 23 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE SOUTHWEST AND FROM KANSAS AND OKLAHOMA TO THE OHIO VALLEY...

...Kansas and Oklahoma to the Ohio Valley...

Unsettled weather will continue, with the footprint for potentially
heavy rain expanding as energy moving through the base of a broad
upper trough interacts with deep moisture that will be supported
persistent southwesterly flow. While models generally agree on a
large footprint of moderate to heavy amounts, they lack agreement
on the details. At least locally heavy amounts are expected,
especially within the western portions of the highlighted area as
a well-defined shortwave dives southeast and is expected to
interact with a pool of deepening moisture along a strong
southwesterly low level jet. Given the indication of 2-3 inches in
some of the models, which is forecast to fall in addition to the
previous days' amounts, an upgrade to a Slight Risk may be
forthcoming if the signal persists and the guidance moves into
better agreement.

...Southwest...

An upper low is forecast to remain cutoff and drift slowly east
along the Southern California coast. Anomalous moisture in place
across Arizona is expected to spread east into parts of New Mexico,
extending the chances for showers and storms, with potentially
heavy amounts into the region.

Pereira
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