839
FOUS30 KWBC 200058
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
858 PM EDT Sat Jul 19 2025

Day 1
Valid 01Z Sun Jul 20 2025 - 12Z Sun Jul 20 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE MID-ATLANTIC AND CENTRAL PLAINS TO MS VALLEY...

...Mid-Atlantic...
One round of heavier convection is moving across eastern VA and
portions of northern NC this evening. Heavy rainfall rates have
been resulting in isolated to scattered instances of flash flooding
with this activity. Another area of more isolated convection is
moving across portions of WV and southwest VA. These cells are
smaller and less organized, but still producing localized heavy
rates and possible flash flooding. The former area of convection
should continue to push offshore and gradually weaken, and so the
flash flood risk from this activity should be on a downward trend.
The convection over WV and VA should also generally follow a
weakening trend this evening into tonight, although this activity
does have some shortwave forcing and stronger moisture transport
associated with it. Thus as it moves eastward tonight and interacts
with some lingering areas of instability, some small scale
convective clusters could persist from WV into VA. Not expecting
anything too organized...but even any small clusters will be
capable of producing heavy rates. Thus an isolated flash flood risk
could persist.

...Central and Northern Plains...
Convection this evening will pose an isolated to scattered flash
flood risk across portions of northern KS into south central NE.
Strong to severe convection has developed over this area near a
stationary front. The environment favors supercells and some
upscale growth of storms. Supercell motions are off to the
southeast, with the deep layer mean wind supporting cell motions
off to the northeast. This supports some cell merging as convection
continues to increase in coverage this evening...and with PWs
increasing towards 2", heavy rainfall rates are likely.

As we head into the overnight hours convection should expand in
coverage from eastern NE into IA near the stationary front. Expect
a broad are of convection to move west to east across IA near this
front bringing a heavy rainfall and flash flood risk. Both the 18z
HREF and 12z REFS have 3" neighborhood probabilities of 40-60%,
and recent runs of the HRRR and RRFS depict narrow swath(s) of
3-5" of rain through the overnight hours. The probability of
exceeding 5" of rain in the HREF/REFS drops off significantly, as
the quick eastward progression of convection should cap the upper
bound of rainfall totals. This axis from far eastern NE into
central IA is considered to be a higher end Slight risk...with
scattered flash flooding likely. This is especially true over
portions of central and eastern IA where soil moisture and
streamflows are already elevated. While the general quick movement
of the convection will hopefully prevent more widespread higher end
impacts...some training near the front will likely result in
scattered flash flood concerns, and locally significant impacts are
possible given the expected rainfall rates and training potential
near the front.

Chenard


Day 2
Valid 12Z Sun Jul 20 2025 - 12Z Mon Jul 21 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
MIDWEST, SOUTHERN APPALACHIANS, & NORTHERN PLAINS...

2030Z Excessive Rainfall Discussion Update...

The corridor from the Upper Midwest/Northern Plains to the Southern
Appalachians continues to be the focus for heavy to potentially
excessive rainfall on Sunday...aligned with the highest
precipitable water/instability axis. In addition...a plume of
moisture moving northward will begin to turn anti-cyclonically
over the Southwest United States helping to spark scattered late
day/evening convection capable of producing locally excessive
rainfall.

Bann


Previous Excessive Rainfall Discussion...

...Midwest, Ohio Valley, & Southern Appalachians...
High moisture persists into Sunday -- precipitable water values
eclipsing 2.25" -- with the core of the instability pool more
significant across portions of the Ohio Valley on Sunday as warming
at 700 hPa occurs across the Central Plains, slowly strengthening
a mid-level capping inversion. Effective bulk shear should remain
sufficient for convective organization. Inflow off the instability
pool could lead to backbuilding, so the potential for 4" amounts in
an hour and local 8" totals remains (the 00z NAM advertised 7").
There`s not enough confidence on where the higher amounts will
materialize to upgrade to a Moderate Risk, but a higher end Slight
Risk appears to exist from in and near southern IL into KY, TN,
southern WV, and westernmost VA. Localized Moderate or High Risk
impacts cannot be ruled out.


...Northern Plains...
Much of North Dakota will be at the nose of a potent low level jet
across the area. A subtle shortwave in the upper level jet may be
all it takes to initiate a line of storms across the region,
though there may be two separate rounds: one in the morning and a
second Sunday night. There is considerable uncertainty both with
storm intensity and receptivity of the ground to the heavy
rainfall. Used the recent guidance to trim some of the Slight Risk
area away. Like continuity, believe this is a lower end Slight
Risk.


Southwest/Southern Rockies...
Enough moisture is available for scattered monsoon convection on
Sunday. Hourly amounts to 2" are possible due to diurnal heating,
which would be most problematic in urban areas, dry washes/arroyos,
or burn scars.


Roth/Wegman


Day 3
Valid 12Z Mon Jul 21 2025 - 12Z Tue Jul 22 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE SOUTHERN ROCKIES, PLAINS, OHIO VALLEY, & SOUTHEAST...

2030Z Excessive Rainfall Discussion Update...
Few changes made with the 12Z numerical guidance showing agreement
with the earlier model runs. Primary concerns remain for flooding
and run off concerns over any burn scars/arroyos or urban areas.

Bann

Previous Excessive Rainfall Discussion...

Surface boundaries/low pressure areas/upper level disturbances are
on this move this period, which along with warming temperatures at
700 hPa/increased mid- level capping across portions of the
Central Plains and IA should broadly limit QPF and flash flood
potential. Wherever cells can manage to train/merge, hourly rain
amounts up to 3" with local totals to 6" would be possible across
the Plains, Ohio Valley, and Southeast, while hourly amounts up to
2" and local totals to 4" would be possible across the Southern
Rockies and Southwest. At the moment, it appears any flash flooding
would be on an isolated to widely scattered basis. In the
Southwest and Southern Rockies, burn scars and dry washes/arroyos
would be most at risk. Anywhere within these regions, urban areas
would be of most concern.

Roth


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