Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Jun 26 2025 19:47:20 AWUS01 KWNH 261945 FFGMPD NJZ000-PAZ000-DEZ000-MDZ000-VAZ000-DCZ000-WVZ000-270145- Mesoscale Precipitation Discussion 0520 NWS Weather Prediction Center College Park MD 344 PM EDT Thu Jun 26 2025 Areas affected...Mid-Atlantic Concerning...Heavy rainfall...Flash flooding possible Valid 261945Z - 270145Z SUMMARY...Increasing number of thunderstorms will producing downpours containing hourly rainfall rates >2"/hr in some cases. Flash flooding is possible in impacted areas, especially areas with saturated soils and within more urbanized communities. DISCUSSION...The Mid-Atlantic is caught between a series of converging surface boundaries. A back-door cold front is approaching from the east, marching through the Delaware Valley and slowly making its way towards the northern neck of the Chesapeake Bay. To the north and west, a stationary front and the added help of a lake breeze off Lake Erie has triggered thunderstorms over northeast Ohio that are tracking southeast into western PA. Plus, strong surface based heating has been unfolding across the region that is causing a burgeoning field of cumulonimbus clouds along the Central Appalachians. The 12Z IAD RAOB showed a convective temp of 93F, which most areas from southeast PA on south through MD and into northern VA have all reached as of 19Z. Storms are initiating within an environment that is likely to have anywhere from 1,000-2,000 J/kg of MLCAPE and PWs that range between 1.75" from western and central PA to >2.0" from the DC/Baltimore area on east to the northern DelMarVa Peninsula. Vertical wind shear soundings show generally weak shear aloft, making storm modes largely pulse-like in nature. However, outflow boundaries emanating from these first batch of storms will fire additional thunderstorms that congeal into larger clusters in parts of the Mid-Atlantic this evening. The 12Z HREF's probabilistic guidance is keying in on the greater DC/Baltimore metro area on north into the Lower Susquehanna Valley with the low-to-moderate chances (30-60%, highest probs in the DC metro area on east to the MD Eastern Shore) for >3" of rainfall between 21-03Z this evening. Farther west, thunderstorms propagating southeast from western OH will be a focus for additional thunderstorm development, as will areas along and north of I-80 where differential heating is becoming more pronounced. Some thunderstorms will be capable of producing >2"/hr rainfall rates given the available instability and moisture parameters, making places with sensitive soils (>80% 0-40cm soil saturation in northern WV, western and central PA) and heavier urbanized environments particularly susceptible to flash flooding this evening. Thunderstorm coverage should begin to fade after 03Z given the marginal vertical wind shear aloft and loss of daytime heating. Mullinax ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!44u1H162CiRzIW4v0puCGh5DcWdvRc6LmTYRYg6EhoYVUNk91MbCXcA34YBafbFdAMhp= d-vo7yqUw7nQpuTKnICS2gE$ for graphic product... ATTN...WFO...AKQ...BGM...CTP...LWX...PBZ...PHI...RLX... ATTN...RFC...RHA...TIR...NWC... LAT...LON 41827623 41367525 40217554 39507507 38347547=20 37847628 37867748 37917902 38597966 40078014=20 40907993 41327907 41587753=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 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .