Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Jul 01 2025 16:34:42 AWUS01 KWNH 011633 FFGMPD NJZ000-PAZ000-DEZ000-MDZ000-VAZ000-DCZ000-WVZ000-012230- Mesoscale Precipitation Discussion 0567 NWS Weather Prediction Center College Park MD 1233 PM EDT Tue Jul 01 2025 Areas affected...Parts of the Central Appalachians and Mid-Atlantic Concerning...Heavy rainfall...Flash flooding likely Valid 011630Z - 012230Z SUMMARY...Widespread showers and thunderstorms are expected this afternoon across the central Appalachians into the Mid-Atlantic within a very moist and unstable environment. Maximum rainfall rates of 2-3"/hr are anticipated and may overlap with the highly urban corridor between Washington D.C. and Philadelphia, as well as compromised terrain in southeast PA due to heavy rainfall last night. Numerous instances of flash flooding are likely, with some significant imapacts possible. DISCUSSION...GOES-East visible satellite imagery depicts a growing cumulus field along the Blue Ridge Mts of northern/central VA through the Mid-Atlantic, with recent LightningCast values spiking along the Blue indicative of convective initiation imminent (seen now on radar after 1610Z). These storms are developing ahead of an upper trough swinging through the Midwest, prompting strengthening west-northwesterly mean layer flow. Additionally, GOES-EAST WV-ML highlights a disturbance off the Southeast coastline which is helping to squeeze mid-to-upper level moisture transport towards the central Appalachians and Mid-Atlantic. PWATs are well above climatology (above the 90th percentile per the 00z ECENS) and even over the daily record for IAD (12z sounding of 2.07"). Additionally, clear skies most of the morning across much of the Mid-Atlantic has allowed for SBCAPE to increase over 4000 J/kg from the central Chesapeake Bay northward into central NJ per SPC's mesoanalysis. The greatest bulk shear remains to the north over PA, but local bay/sea breezes and terrain should help developing updrafts organize and maintain strength. Additionally, the mean layer west-northwesterly flow will allow for repeating cells in this direction as leading convection eventually merges with activity progressing over the central Appalachians. Rainfall rates are likely to be very intense within the available environment and produce hourly rates up to 3", with instantaneous rates even higher. The limiting factor remains if convection can remain progressive, which would reduce the potential rainfall totals but not limit the impacts from rainfall rates alone. Southeast PA in particular is extremely susceptible to these intense rainfall rates as 1-hr FFG in the area is below 1". It is this region, and the highly urbanized locations, where significant impacts are most likely should convection overlap and rainfall amounts maximize the available environment. Elsewhere across the Mid-Atlantic, scattered to numerous instances of flash flooding are also likely, but progressive west-northwesterly storm motions should limit severity. Snell ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!_tULk7ArSfYZoKFHpQZiGsb0fKAJSZ5cGT6wyCiRur84oXeUcLoOTtQK85VqMTkBX1En= KRQakoOpCamDAvpG9yXfC-g$ for graphic product... ATTN...WFO...AKQ...CTP...LWX...PBZ...PHI...RLX...RNK... ATTN...RFC...RHA...TIR...NWC... LAT...LON 40867651 40597506 40107395 39557406 39207530=20 38927633 38337757 37837852 37817937 38277981=20 39397947 40447886 40857783=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) .