Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
349 PM EDT Sat Aug 15 2026
Day 2
Valid 12Z Sun Aug 16 2026 - 12Z Mon Aug 17 2026

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
WEST VIRGINIA...

20Z Update...
Similar to Day 1, the HREF and REFS ensemble suites did not show
reason to make any large changes to the overnight issuance. Minor
adjustments included a small expansion of the Moderate Risk farther
south along the upslope of the southern WV mountains, where
additional QPF has been increasing in this flood-vulnerable area.
Farther downstream, extended the Slight Risk into south-central
Virginia. While there are difference in the details, there are
enough members of the HREF and REFS guidance showing repeating
storms dropping southeast of the mountains to raise probabilities
for amounts over 3 inches to over 40 percent within the region.
Back to the west, the consensus of the guidance showed enough of a
decrease in QPF that the western extent of the Slight Risk was
trimmed out of parts of the OH Valley.

Pereira

Previous Discussion...
...OH Valley into the Mid-Atlantic...
A Moderate risk upgrade has been issued for portions of WV.
Persistent and strong westerly 850mb moisture transport impinging
into the complex terrain is concerning, favoring convective
training and/or repeat activity. This setup, combined with PW
values forecast to exceed 2", supports the potential for numerous
instances of flash flooding. An initial round of convection should
be ongoing at 12z Sunday with an active training/backbuilding
threat. While a relative lull in coverage may occur after this,
activity is expected to ramp back up by afternoon into the evening
along and ahead of an approaching cold front. While this latter
activity may lean more progressive the high PW airmass could
easily yield a quick 1-3" of additional rainfall. Given that soil
conditions will likely be quite saturated by this time,
considerable flash flooding impacts are a distinct possibility in
and near the terrain of WV. While some uncertainty with the details
exist, the 00z Gem reg, RRFS, REFS hit this area with over 3" of
rain.

A Slight risk extends eastward across PA, MD, NJ, DE and northern
VA. A mid level shortwave/MCV, alongside the synoptic cold front,
will provide ample forcing for convection across the region. PWs
increasing towards 2.3" and strong low level moisture transport
will create an environment conducive to heavy rainfall rates. An
MCS approaching from the west at 12z Sunday may tend to weaken as
it outruns the primary instability axis, but additional convective
initiation is expected in its wake as instability and moisture
increase ahead of the front. While the cold front will eventually
push the convection along, the environment ahead of the front will
be favorable for backbuilding/training with weak Corfidi vectors.
Any training will pose a flash flood risk, particularly over
sensitive urban corridors. The Slight risk was adjusted southward
to align with guidance trends, with the 00z RRFS and REFS matching
well with the AIGFS/AIFS axis.

The Slight risk was also expanded westward into the OH Valley to
account for additional convection over saturated soil conditions.
Additional convection is expected along/ahead of the advancing
cold front within an airmass characterized by CAPE exceeding 3000
J/kg and PWs near or just over 2". While individual cells should
move more quickly compared to previous days, the saturated
conditions mean even progressive heavy rates will produce scattered
flash flood impacts.

...Southwest...
A Slight risk continues from northeast NM into southeast CO,
focused along and north of a cold front where low level convergence
and easterly upslope flow are maximized beneath upper level right
entrance jet dynamics.

While PW values are not extremely high, they remain slightly above
average, and ample instability will compensate to support isolated
to scattered flash flooding from slow moving cells and cell
mergers. Guidance from the AIGFS, RRFS, and REFS is in good
agreement with this spatial placement.

Chenard


Day 2 threat area: www.wpc.ncep.noaa.gov/qpf/98epoints.txt