Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Jul 25 2023 15:34:14 AWUS01 KWNH 251534 FFGMPD CTZ000-NYZ000-NJZ000-PAZ000-DEZ000-MDZ000-VAZ000-DCZ000-252100- Mesoscale Precipitation Discussion 0791 NWS Weather Prediction Center College Park MD 1133 AM EDT Tue Jul 25 2023 Areas affected...Eastern PA...DE...NJ...Southeastern NY...Southwest CT...Central & Eastern MD...DC... Concerning...Heavy rainfall...Flash flooding possible Valid 251530Z - 252100Z SUMMARY...Strong thunderstorms with intense rain-rates crossing urban locations pose localized possible flash flooding. Some cells may remain fairly stationary due to redevelopment along favored convergence in proximity to Bays/Harbors/Sounds. DISCUSSION...An impressive shortwave continues to cross central PA with a trailing trough starting to cross central MD into NoVA providing favorable DPVA vertical ascent across the Mid-Atlantic. GOES-E 1-minute imagery loop shows expanding cu field within the southeast quadrant of the circulation over eastern Central MD, the Delmarva Peninsula, SE PA into NJ, generally coincident with enhanced low level moisture and nearly full morning insolation.=20 MLCAPEs are over 2000 J/kg and CIRA LPW shows enhanced surface to 850mb values of .9-1" starting to be over-topped by leading edge of 700-500mb moisture associated with the trailing mid-level trof...where values of .25 will increase to near .4" over the next few hours. Overall result is a corridor of 1.75" extending along I-95 from DC to Philly (cu field is a good proxy) up to 1.5" near N NJ/NYC. Southerly to south-southeasterly flow in the low-levels is starting to converge on favored bays/inlets sparking some early thunderstorm development. While core of cells will track northeast, continued/strengthening surface flow across the bay/inlets should support effective back-building. Initially rate of 1-1.5"/hr may uptick toward 2" as initial downdrafts moisten the column. As such, localized spots of 2-3" will be possible along these localized convergence hotspots. Toward 17-18z, a bit more heating and stronger DPVA/mid-level convergence should spark scattered thunderstorm development concentrated across N MD/SE PA. Low level moisture convergence should increase across the unstable air resulting in increased scattered development. Deep layer southwesterly flow aloft and low level inflow suggests ENE propagation at 15-20kts, likely limiting duration of any given downdraft. However, moisture flux convergence and ample deep layer moisture should allow for intense short-term rates. 12z HRRR suggests 1-1.25" totals in a 15 minute period with spots of 2"/hr. Spots of HREF probability of 20-30% of 2"/hr across the Lower Hudson to Potomac provide some confidence for this scattered intense nature. Proximity to the urban centers/hydrophobic grounds will result in increased run-off resulting in greatest possibility for localized flash flooding. Gallina ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!6mp5U-jHrf2XaQXSoSMVYmRzXtozNRr7fsJf55RB_QPKleAzaFpPJGFGtErZ159xL1Yu= xUkZ3u0lOTRVgOtEJ1Nxyjw$ for graphic product... ATTN...WFO...AKQ...BGM...CTP...LWX...OKX...PHI... ATTN...RFC...MARFC...NERFC...NWC... LAT...LON 41477534 41417398 41347328 40727353 39667406=20 38577491 38247541 38467684 38987714 39707677=20 40587629 41307582=20 =3D =3D =3D To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM. --- SBBSecho 3.14-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .