Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Jun 30 2025 17:54:54 AWUS01 KWNH 301754 FFGMPD NJZ000-PAZ000-DEZ000-MDZ000-302200- Mesoscale Precipitation Discussion 0559 NWS Weather Prediction Center College Park MD 154 PM EDT Mon Jun 30 2025 Areas affected...Southeast Pennsylvania, Southern and Central New Jersey, and Delaware Concerning...Heavy rainfall...Flash flooding possible Valid 301752Z - 302200Z Summary...Isolated to scattered thunderstorms will continue early this afternoon in southeast Pennsylvania, southern and central New Jersey, and portions of Delaware. At times, these thunderstorms may move very slowly or become nearly stationary, which would lead to localized areas of very heavy rainfall and potentially flash flooding, especially if that occurs over urban areas. The threat of flash flooding should be highest through around 5-6 PM EDT, but could last longer. Discussion...Several well-organized thunderstorms have developed in an area of strong instability from SE PA into S NJ and DE. Hi-res model guidance has struggled with this, but the experimental RRFS may be doing the best as of 1730Z. It shows organized but isolated cells or small clusters persisting across the area through about 22Z (6 PM EDT), anchoring at times to sea breeze boundaries or a front draped across the region. There is some evidence of this already happening with a thunderstorm near coastal Sussex County, Delaware, and it could conceivably happen with other storms elsewhere in the region. The environment is very supportive of intense rain rates with PWs near or above 2 inches (above the 95th percentile for late June) and very strong instability. Therefore, hourly rainfall in excess of 2 inches is plausible and if storms stall in a given location for over an hour, rapid development of rainfall maxima over 3-4 inches would be possible. In these areas, flash flooding could develop, particularly if it intersects with urban areas. The outlook beyond 21-22Z (5-6 PM EDT) is less certain, as the hi-res model guidance doesn't look to be completely reliable. It seems doubtful that all the instability in the region would be completely exhausted by that time, so a continuation of the flash flood threat could continue into the early evening. However, the threat may shift to areas just outside where initial development is occurring. Lamers ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!-ikzzo3BcEBkJ5Yx9c5lyDTmlbXGWCTsyOCFkQYjxBt_tCvvW41MUTQJOU15BIsiEHIh= n6TnJqEPgwu14Ii9wlPhU4M$ for graphic product... ATTN...WFO...AKQ...CTP...PHI... ATTN...RFC...RHA...NWC... LAT...LON 40897571 40737499 40397396 39817396 39407463=20 38997486 38377496 38457537 38977564 39537578=20 39827614 40147705 40807667=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) .