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Mesoscale Precipitation Discussion 1006

Status

Issued Active alert

Start Time

Wed 09/22/2021 01:36 PM EDT

End Time

Wed 09/22/2021 07:35 PM EDT

Impacts

Informational

Locations Affected

Pittsburgh, PA ∙ Akron, OH ∙ Canton, OH ∙ Youngstown, OH ∙ Struthers, OH ∙ Dundee, OH ∙ Highcliff, PA ∙ Jamestown, PA ∙ Barnesville, OH ∙ Silver Lake, OH

Full Alert Message

Mesoscale Precipitation Discussion 1006 NWS Weather Prediction Center College Park MD 136 PM EDT Wed Sep 22 2021 Areas affected...eastern OH, northern WV into western PA Concerning...Heavy rainfall...Flash flooding possible Valid 221735Z - 222335Z Summary...Flash flooding will be possible across portions of the Allegheny Plateau into portions of the Appalachians through early evening. Rainfall rates of 1-2 in/hr and brief cell mergers are expected to support a few 2-3 inch totals through 00Z. Discussion...17Z surface observations placed a low in OH, just northwest of ZZV, and an associated cold front extending southward from the low through WV and western VA. A second low attached to the front was analyzed over Lake Erie. Visible satellite imagery indicated an area of building cumulus within an area of clearing noted over northern WV into eastern OH and western PA where dewpoints ranged from 65 to 70 degrees, supporting precipitable water values of 1.4 to 1.8 inches (+2 standardized anomalies). The 17Z SPC mesoanalysis showed 500-1000 J/kg MLCAPE over northern WV into southwestern PA, with continued heating likely to support an expansion of the instability field toward the north into the afternoon. Widely scattered thunderstorms are expected to develop over the next 1-3 hours within the warm sector of the frontal system with continued daytime heating as any lower level inhibition has likely eroded by now. However, rapid thunderstorm development is expected immediately ahead of the cold front in the 20-22Z time frame which should generally move from south to north at 30-40 kt with the deeper-layer mean flow, but as the OH surface low tracks NNE over the next 6 hours, 925-850 mb flow is forecast to back slightly across PA which will delay the eastward translation of deep-layered moisture. Rainfall rates of 1-2 in/hr will be possible given the potential for brief south to north training of heavy rain cores. This may lead to a few 2-3 inch rainfall totals and areas of flash flooding through 00Z. Otto ...Please see www.wpc.ncep.noaa.gov for graphic product... ATTN...WFO...CLE...CTP...PBZ...RLX... ATTN...RFC...OHRFC...NWC... LAT...LON 42078016 41757961 41417941 40787924 39877920 39147978 38958056 39258148 40278175 41208162 41648131 42018088