188
FOUS30 KWBC 190108
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
908 PM EDT Fri Jul 18 2025

Day 1
Valid 01Z Sat Jul 19 2025 - 12Z Sat Jul 19 2025

...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF
THE MID-ATLANTIC, OHIO VALLEY, NORTHERN PLAINS AND SOUTHWEST...

...Mid-Atlantic...
A Slight risk remains for much of eastern VA into northeast NC.
Convection near a backdoor front will continue to pose some flash
flood risk into the evening hours. Cells are generally moving quick
enough to limit the magnitude and extent of impacts...however with
PWs around 2.3" rainfall rate potential remains very high. So even
some brief backbuilding and/or merging of cells will likely be
enough to get a quick 2-3" of rain. Thus scattered flash flooding
remains likely over the next few hours as convection continues to
move eastward, with the risk expected to decline as we get into the
overnight hours.

...OH Valley...
We will carry a small Slight risk across portions of KY and TN
where some training of cells has resulted in a more focused area
of scattered flash flood warnings this evening. One area of slower
cell movement near the stationary front over KY, and another over
northern TN where just enough low level southerly inflow is
resulting in some backbuilding of cells. Both areas are probably
peaking now or will shortly, with the risk gradually decreasing as
instability is eroded tonight.

....Plains to Upper Midwest...
A Slight risk remains across portions of southeast SD, northeast
NE, southern MN and much of central and northern IA. Convection is
expected to increase in coverage and magnitude through the evening
hours, with upscale growth into a couple clusters or MCS during the
overnight hours. Initially cell movement will be off to the east,
but as convection organizes it will likely take a turn off to the
southeast. As this is occurring we could see enough of a training
component to result in isolated to scattered flash flood concerns.
The same can be said on the southwest flank of the eventual MCS or
convective cluster, with backbuilding into the low level jet
supporting some flash flood potential. The overall cell motions
will be quick enough to keep flash flood coverage and magnitude
down...however recent runs of both the HRRR and RRFS indicate a
swath of over 3" of rain...much of which will likely fall in an
hour or two. This should be enough to result in isolated to
scattered instances of flash flooding...especially across any more
susceptible low lying or urban areas.

...Southwest...
Maintained a Slight risk across portions of far southeast AZ into
southern NM where convective coverage still supports an isolated
to scattered flash flood risk for a couple more hours. Otherwise a
Marginal risk remains for a broader portion of NM and portions of
NV and UT where convective coverage and intensity are generally on
a downward trend, however a localized flash flood persists.

Chenard


Day 2
Valid 12Z Sat Jul 19 2025 - 12Z Sun Jul 20 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
MIDWEST INTO THE TENNESSEE VALLEY AND THE SOUTHERN MID-ATLANTIC...

21Z update...

Campbell

Ample tropical moisture, at least in part associated with the plume
of moisture associated with the low over Louisiana will stream
northeastward on a continuous low level jet. As that moisture runs
into a stationary front set up over the Midwest, it will be lifted,
resulting in numerous showers and thunderstorms all across the
region. The guidance is in poor agreement as to how those
thunderstorms will organize. What appears most probable is the
cluster of thunderstorms from the upper Midwest on Day 1/Friday
will continue southeastward along the front, able to easily sustain
itself due to the abundant tropical moisture in place across much
of the eastern half of the US.

With daytime heating, clusters of showers and thunderstorms will
develop ahead of this aforementioned line. Cell mergers and the
eventual congealing of the storms with the line will allow quite a
few areas across the Midwest to have multiple rounds of storms to
impact the area. This will likely result in widely scattered to
scattered instances of flash flooding. Areas hard hit with heavy
rainfall in previous days would be particularly vulnerable to
additional flash flooding should multiple rounds of storms move
over those communities.

Wegman

Day 3
Valid 12Z Sun Jul 20 2025 - 12Z Mon Jul 21 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
MIDWEST AND NORTHERN PLAINS...

...Midwest and the Ohio/Tennessee Valleys...

21Z update... The latest guidance suggested a small uptick in QPF
over Iowa so made a small westward expansion of the Slight in that
vicinity. Also the southward trend previously noted (below) also
warranted a minor southward expansion of the Slight Risk into far
northern Alabama and Georgia.

Campbell

A complex setup looks to unfold across this region on Sunday. A
line of storms will move southeastward from the Mississippi River
Valley across the Ohio Valley. With ample daytime heating and a
stationary front still in place. Widespread thunderstorms will
develop along the frontal interface. The storms will interact with
each other, likely congealing into clusters as the line absorbs the
storms from northwest to southeast. Behind this line however,
additional storms are likely to develop overnight Sunday night,
especially for western areas in Iowa and Illinois. The slow moving
nature of the storms at the nose of the jet will increase the flash
flooding threat in that region as well. Further, all of the Slight
Risk area will have been through storms from the Day 2/Saturday
period, so soils are likely to be more responsive to flash flooding
should storms occur in these same areas again on Sunday. There is
some uncertainty as to where the storms will align, which will
depend on frontal position. Much of the guidance has trended a bit
southwestward, so the Slight was trimmed out of northern Indiana
and Illinois with this update in favor of the central portions of
those same states. Into Kentucky and the western Virginias, terrain
and recent heavy rainfall increase the flash flooding threat
further in these areas, where a higher end Slight remains in
effect.

...Northern Plains...

21Z update... No significant differences noted in the latest guidance
that would suggest an adjustment to the Slight or Marginal Risk
ares over the Dakotas.

Campbell

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,
especially Sunday night, 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. Due to this uncertainty, the Slight Risk
area was left unchanged with this update, but is considered a lower
end Slight.

Wegman


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