506
AWUS01 KWNH 251851
FFGMPD
NYZ000-PAZ000-MDZ000-VAZ000-WVZ000-OHZ000-260050-

Mesoscale Precipitation Discussion 0322
NWS Weather Prediction Center College Park MD
250 PM EDT Sat May 25 2024

Areas affected...Far Southeast OH...Northern and Eastern WV...Far
Northwest VA...Western MD...Central and Western PA...Southern NY

Concerning...Heavy rainfall...Flash flooding possible

Valid 251850Z - 260050Z

SUMMARY...Increasing coverage of showers and thunderstorms is
expected this afternoon and into this evening. Some relatively
slow-moving cells will be capable of producing locally heavy
rainfall and an isolated threat for flash flooding.

DISCUSSION...Satellite and radar imagery already shows a broken
axis of showers and thunderstorms gradually expanding in coverage
across western PA and into southern NY. The activity is forming in
a relatively moist and unstable airmass characterized by MLCAPE
values that have risen to 1000 to 1500+ J/kg and with PWs locally
as high as 1.2 to 1.4 inches. The greatest concentration of
moisture and instability is currently pooled across eastern OH and
western PA out ahead of an approaching cold front.

A shortwave trough crossing through the Great Lakes region will be
responsible for advancing this cold front gradually off to the
east this afternoon and evening which coupled with the
thermodynamic environment should favor an additional expansion of
convection off to the east and south including areas from southern
NY through central PA and also to the southwest across the MD/WV
panhandles and adjacent areas of northern WV and southeast OH.

The early to mid-afternoon visible satellite imagery shows an
expanding field of moderate CU and some TCU across southeast OH
and southwest PA and this is suggestive of convective initiation
soon taking place as additional surface heating/solar insolation
further destabilizes the boundary layer.

Rainfall rates with the stronger storms are expected to reach 1.5+
inches/hour, and with some of the cells tending to be rather
slow-moving and locally repeating over the same area, some spotty
storm total amounts of 2 to 3+ inches will be possible.

This coupled with relatively moist antecedent conditions suggest
an isolated threat of flash flooding will be possible this
afternoon and into the evening hours. The more urbanized locations
will be most susceptible to runoff problems.

Orrison

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

ATTN...WFO...BGM...BUF...CTP...LWX...PBZ...RLX...

ATTN...RFC...MARFC...NERFC...OHRFC...NWC...

LAT...LON   42977698 42927614 42667587 42077606 41437628
            40187695 39387774 38877876 38748054 38978152
            39418176 39938165 40528105 41068006 42387793