458
AWUS01 KWNH 132059
FFGMPD
CTZ000-NYZ000-NJZ000-PAZ000-DEZ000-MDZ000-VAZ000-DCZ000-WVZ000-OHZ000-140255-

Mesoscale Precipitation Discussion 0929
NWS Weather Prediction Center College Park MD
455 PM EDT Wed Aug 13 2025

Areas affected...Portions of the Central Appalachians and into the
Central/Northern Mid-Atlantic and Southern New England

Concerning...Heavy rainfall...Flash flooding likely

Valid 132055Z - 140255Z

SUMMARY...Clusters of heavy showers and thunderstorms with locally
extreme rainfall rates will continue going into the evening hours
across the interior of the central and northern Mid-Atlantic
region. Scattered areas of flash flooding will be likely which
will include strong concerns for urban flash flooding impacts near
and along the I-95 corridor.

DISCUSSION...The latest satellite and radar imagery shows clusters
of heavy showers and thunderstorms impacting central to northern
VA with some recent development noted across central MD. Meanwhile
farther off to the northeast, there are locally more organized
clusters of cold-topped convection seen impacting eastern PA.

The convection continues to be associated with the leading edge of
an elongated mid-level shear axis/vort center while interacting
with a very moist and strongly unstable airmass that has pooled
across much of the Mid-Atlantic region east of the Blue Ridge.
MLCAPE values of 2000 to 2500 J/kg are noted across central VA up
through southeast PA with some uptick in low-level moisture
convergence noted across the region over the last hour including
the middle and upper parts of the Chesapeake Bay area. The PWs are
very high and locally over 2 standard deviations above normal,
with values of 2.0 to 2.25 inches in place.

Early morning RAOB soundings showed tall skinny CAPE profiles and
elevated WBZ/freezing levels. This again strongly supports a very
efficient and tropical environment that will promote highly
efficient processes for extreme rainfall rate potential. Already
some of the stronger storm clusters have been producing rainfall
rates well into the 2 to 3 inch/hour range.

Convection should tend to generally build off to the east through
this evening into portions of the I-95 corridor from near
Washington D.C up through Philadelphia and then on up to at least
near the New York City metropolitan area. Meanwhile, the southwest
flank of the MPD area involving central VA back westward into the
central Appalachians will remain an area for convection as well
given proximity of a well-defined outflow boundary. Radar shows
locally concentrated areas of heavy thunderstorms across these
areas.

Localized/spotty additional rainfall totals of 3 to 4+ inches will
still be possible going through the evening hours. This will
likely promote scattered areas of flash flooding with concerns for
potentially considerable urban flooding impacts if some of the
heavier rainfall totals materialize over some of the larger
metropolitan areas.

Orrison

...Please see www.wpc.ncep.noaa.gov for graphic product...

ATTN...WFO...AKQ...ALY...BOX...CTP...LWX...OKX...PHI...RLX...
RNK...

ATTN...RFC...RHA...TAR...TIR...NWC...

LAT...LON   41947338 41577241 39937358 38537549 37567763
            37528000 37888137 38608217 39168190 39228076
            38897995 38717888 39177744 40247621 41017485