Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Jul 08 2025 18:24:52 AWUS01 KWNH 081824 FFGMPD NJZ000-PAZ000-DEZ000-MDZ000-VAZ000-DCZ000-WVZ000-090000- Mesoscale Precipitation Discussion 0620 NWS Weather Prediction Center College Park MD 224 PM EDT Tue Jul 08 2025 Areas affected...Mid-Atlantic States Concerning...Heavy rainfall...Flash flooding possible Valid 081823Z - 090000Z Summary...Showers and thunderstorms will expand across the Mid-Atlantic ahead of a cold front through this evening. Rainfall rates at times could reach 3"/hr, which through repeating rounds could produce 1-3" of rain. Flash flooding is possible. Discussion...The regional radar mosaic this afternoon shows a rapid expansion of higher reflectivity associated with an increasing coverage of thunderstorms from West Virginia into eastern Pennsylvania. These thunderstorms are blossoming ahead of a cold front which is approaching from the west, with a weak shortwave noted in GOES-E WV imagery moving across central Pennsylvania as well. This area is additionally in the favorable RRQ of a modest jet streak pivoting over the Northeast, enhancing deep layer ascent. This lift is impinging into impressive thermodynamics with a ribbon of MLCAPE exceeding 2500 J/kg being drawn northward into the DelMarva and 2000 J/kg reaching into much of PA on 850mb inflow of 15-20 kts. which is also pushing elevated PWs of 1.8-1.9 inches into the region. The 12Z U/A sounding out of IAD also measured a WBZ level of nearly 14,000 feet, well above the 90th percentile and approaching the daily record. This all suggests an environment which will support efficient warm-rain processes today, and recent radar-estimated rain rates from KCCX have been above 1.5"/hr. As the aftn progresses and the front and the accompanying ascent push into the destabilizing environment, thunderstorms should become more widespread. The mean 0-6km wind will remain progressive at around 20 kts to the E/NE, suggesting cells will continue to track steadily to the east, but the presence of the shortwave aloft and modest 20 kts of bulk shear could force subtle organization into clusters. More problematic will be the rainfall rates, for which both the REFS and HREF suggest have a 20-40% chance of exceeding 2"/hr, and HRRR 15-min rainfall is as high as 0.75" indicating brief 3+"/hr rates. Even if storms remain progressive, this could be problematic as these intense rates would overwhelm soils leading to runoff, especially in urban areas. However, in some locations repeating rounds may occur as well, leading to total rainfall that has a 15-25% chance of reaching 3" in some areas this evening. Additionally, soils across the area (using NASA SPoRT 0-10cm soil percentile as proxy) have saturation that is generally normal to well above normal from 7-day rainfall that has been as much as 150-300% of normal. This has locally compromised 3-hr FFG to as low as 1.5"/3hrs, especially between Washington, D.C. and Philadelphia, with a secondary minimum near the Shenandoah Valley. Although these heavy rain rates could be problematic anywhere across the area through the evening, it is these more sensitive soils or urban areas that have the greatest risk for impacts. Weiss ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!_iGWa40FIUaXyZ66c26fMfW9QUtYKRzHrdFaJkfYLa_S6ATUWh1pWXL-ZBz7GizTVXvG= 1VnWsXdEkYsxhj_0ZL6zjRE$ for graphic product... ATTN...WFO...AKQ...BGM...CTP...LWX...PBZ...PHI...RLX...RNK... ATTN...RFC...ALR...RHA...TIR...NWC... LAT...LON 41137619 40997535 40627494 40027499 39597540=20 39107581 38597611 38127634 37727668 37377725=20 37187831 37277990 37888073 38298112 38678096=20 38998038 39387942 39857856 40547766 41007701=20 =20=20=20=20=20=20=20=20=20=20=20=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) .