630
AWUS01 KWNH 122356
FFGMPD
NYZ000-PAZ000-MDZ000-VAZ000-WVZ000-OHZ000-KYZ000-130555-

Mesoscale Precipitation Discussion 1265
NWS Weather Prediction Center College Park MD
755 PM EDT Sat Sep 12 2026

Areas affected...Portions of the Upper OH Valley...Central
Appalachians...Northern Mid-Atlantic

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

Valid 122355Z - 130555Z

SUMMARY...Additional areas of heavy showers and thunderstorms are
expected going into the overnight hours. Wet/sensitive antecedent
conditions and locally persistent areas of high rainfall rates
will continue to drive areas of flash flooding.

DISCUSSION...The early evening GOES-E IR/WV satellite imagery
shows a well-defined mid-level shortwave trough advancing east
across the OH Valley which will advance into areas of the central
Appalachians and Mid-Atlantic states overnight. This has been
fostering cold convective tops and an expansive axis of heavy
showers and thunderstorms over the last several hours across
portions of central and northern WV and western PA.

A focused corridor of warm air advection along with deep layer
moisture transport, moderate instability, and shortwave dynamics
are all working in tandem to drive the convective threat across
the region. Ahead of the shortwave trough itself, warm-sector
MLCAPE values of 1000+ J/kg are still in place, with the leading
edge of this up into southwest PA and extendind down through
central WV and back west into central and southern OH. Meanwhile
the northeast advance of a warm front is also allowing for deeper
layer moisture transport and higher PWs to arrive with values
generally near 2 inches.

Over the next several hours heading into the overnight period,
stronger DPVA and associated right-entrance region upper jet
dynamics aloft will support stronger deep layer ascent overrunning
areas of the upper OH Valley, central Appalachians and northern
Mid-Atlantic region as deeper layer moisture transport and warm
air advection continues. This will interact with the remaining
pool of instability over the region and coupled with convergence
along the advancing warm front and orographics/upslope flow near
the higher terrain to maintain regional clusters of heavy showers
and thunderstorms. This may include some northeast advance into
areas of northern PA and southern NY.

Despite gradually waning instability profiles with the loss of
daytime heating, the very moist column coupled with deep layer
forcing will still support high rainfall rates upwards of 1 to 2
inches/hour. This is support by a consensus of the 18Z HREF/REFS
guidance, and the latest multi-model consensus also suggests
corridors of additional cell-training that may yield additional
localized swaths of 2 to 4 inch rainfall totals going through at
least midnight.

Given the ongoing areas of flash flooding and already
wet/sensitive conditions otherwise, these additional rains going
into the overnight hours are likely to promote additional areas of
flash flooding.

Orrison

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

ATTN...WFO...BGM...BUF...CLE...CTP...ILN...JKL...LWX...PBZ...
RLX...RNK...

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

LAT...LON   42857673 42767548 42067522 41427599 40747688
            40017790 38637937 37558059 37318160 37708256
            38338306 39268294 40208205 41318044 42307859