AWUS01 KWNH 211806
FFGMPD
PAZ000-WVZ000-OHZ000-212200-

Mesoscale Precipitation Discussion 0302
NWS Weather Prediction Center College Park MD
204 PM EDT Wed May 21 2025

Areas affected...Northeast Ohio...Western Pennsylvania...Far
Northern West Virginia...

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

Valid 211800Z - 212200Z

Summary...Isolated to scattered instances of flash flooding are
possible, driven by localized hourly totals up to 1-2" and the
potential for 3-hr localized totals in excess of 2".

Discussion...Convection is blossoming this afternoon in the
vicinity of the triple point of a surface cyclone, both within the
warm sector/along the warm front and pivoting northwestward to the
north of the center of the low. The mesoscale environment is
characterized by a ridge of surface ThetaE of 330-336K,
precipitable water of 1.0-1.2 inches (near the 90th percentile,
per PIT sounding climatology), SBCAPE of 500-1500 J/kg, and deep
layer (0-6km) shear of 35-55 kts. While current convection is
moving at a decent clip within 30-40 deep layer (850-300 mb) flow
(resulting in localized hourly maxima near 1.0", despite
instantaneous rates as high as 2.0-2.5", per MRMS estimates),
nearly unidirectional deep layer southwesterly flow (with 850 mb
winds of 15-25 kts) could result in slower storm motions via
upwind propagation should cold pools become more established (per
upwind Corfidi vectors of 10-20 kts towards the east). Along with
cell mergers and localized training segments, this may result in
some localized hourly totals of up to 1-2" (as depicted by recent
hourly HRRR and experimental RRFS runs, as well as the PMM of the
12z HREF) with 3-hr totals 2"+ possible (per 12z HREF 40-km
neighborhood probabilities of 20-30% for 2"/3-hr exceedance).
Isolated to scattered instances of flash flooding are possible
(with 12z HREF 40-km neighborhood probabilities for 1-hr and 3-hr
FFG exceedance ranging from 30-40%, and generally maximized in the
vicinity of the more sensitive Pittsburgh metro area).

Churchill

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

ATTN...WFO...CLE...ILN...PBZ...RLX...

ATTN...RFC...TIR...NWC...

LAT...LON   42048009 41407950 40597928 39747949 39427978 
            39178083 39368145 39728182 40208228 40558272 
            40798300 41178314 41478284 41538235 41798142 
            41908102