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FOUS30 KWBC 261554
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1154 AM EDT Sat Jul 26 2025

Day 1
Valid 16Z Sat Jul 26 2025 - 12Z Sun Jul 27 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PARTS OF
THE SOUTHERN GREAT LAKES AND PENNSYLVANIA...

16Z... In coordination with the New offices an upgrade to a Slight
Risk was made for the rest of the period. The PW values will be
near a daily max and certainly could fuel locally enhanced rain
rates leading to isolated flash flooding, especially over
sensitive terrain. The Slight spans across central/eastern New
York. The Slight over much of Pennsylvania was broadened a little
in a NW to SE fashion. The latest guidance depicts higher rainfall
rates for far northeast Ohio/northwest Pennsylvania than previous
forecast and for western portions of Ohio.

Campbell

Heavy to excessive rainfall is possible along a corridor associated
with vort energy embedded within mid-level flow which was interacting
with a quasi- stationary front and a modestly unstable, but very
moist airmass pooled along it.The continuous influx of high PW
values over this boundary will aid in locally enhanced rainfall.
In addition...the winds aloft will be favorable for training and
backbuilding of storms over recently wet soils. This will elevate
the risk for localized flash flooding, especially for the flash
prone areas within the terrain of Pennsylvania and surrounding
locations. Given the amount of rain that fell in parts of Illinois
on Friday and in the overnight period from Friday night into early
this morning prior to the start of the Day 1 period...introduced a
Slight risk area in addition to the one that was already issued.

...Gulf Coast...

The disorganized area of showers and thunderstorms associated with
a trough of low pressure situated across the western half of the
Gulf will make its way inland over southeast Texas today. Deep
moisture/high precipitable water values and mid- and upper level
forcing continue producing downpours across the central and
western Gulf coast with an emphasis on the immediate coastal plain.

...Northern Plains...

16Z update... Current observations show organized convection
tracking across Minnesota with a renewal of thunderstorm
development this afternoon and evening for the Dakotas and
Minnesota. Guidance is depicting the line of storms to progress
further east which is outside of the morning issuance of the
Marginal Risk. The eastern boundary was adjusted eastward to
account for this trend.

Campbell

The next in a series of potent shortwaves will eject eastward
across the northern tier of states of the Northern
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...although minor nudges were made based on the latest
guidance.

...Northeastern California and Northwest Nevada...

Almost a carbon copy of the prior period for convective impacts
lingering across the Northern Sierra up through northeastern
California and northwest Oregon. The upper pattern is pretty slow
to breakdown with the diffluent area in the longwave setup still
situated over northern California into Nevada. 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 2
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 and Upper Midwest...

The 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. Convection early in the period looks to
be progressive enough to preclude much thereat of excessive
rainfall. However...there should be a weak boundary to the
southwest of the initial convection track with stronger
instability to the south. The instability and the shear set up a
scenario where additional convection will be more capable of
producing heavy to potentially excessive rainfall. Opted to
maintain a the previously issued Slight risk area after shifting
the area eastward.

...The Ohio Valley and Mid Atlantic to southern New England...
Mid-level flow flattens over the Great Lakes and Ohio
Valley...allowing embedded shortwave energy to start propagating
eastward. With the center of the upper high expected to shift just
far enough eastward...some weak height falls will allow shortwave
energy to dig over parts of the Mid-Atlantic. With an anomalously
moist air mass in place...convection with localized downpours have
a low-end threat to result in 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

Day 3
Valid 12Z Mon Jul 28 2025 - 12Z Tue Jul 29 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM THE NORTHERN
HIGH PLAINS INTO THE UPPER MIDWEST AND ACROSS PARTS OF THE
SOUTHWEST UNITED STATES...

...Plains of Eastern Montana to parts of the Upper Midwest...
Showers and thunderstorms capable of producing excessive rainfall
are possible on Monday and Monday night from the plains of Montana
southeastward into parts of the Upper Midwest as surface/low level
flow accelerates between low pressure to the south and high
pressure strengthening over southern Canada. Development of surface
low pressure over southwest South Dakota/northwest Nebraska
results in moisture transport up and over the boundary...leading to
a better chance for enhanced rainfall rates from the Dakotas into
Minnesota or Iowa. Farther west...there should be a feed of
moisture and some instability in the easterly flow into eastern
Montana. Given considerable uncertainty...not incline for more than
a Marginal risk area.


...Southwest US...
A continuation of deeper moisture transport into the Southwest US
will linger into Monday...with a continued chance for scattered
late day and evening convection across parts of New Mexico and a
small portion of Arizona that extends northward along the southern
and central Colorado front range.

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