Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Jun 27 2025 20:36:49 AWUS01 KWNH 272035 FFGMPD VAZ000-NCZ000-WVZ000-SCZ000-OHZ000-GAZ000-TNZ000-KYZ000-280230- Mesoscale Precipitation Discussion 0532 NWS Weather Prediction Center College Park MD 434 PM EDT Fri Jun 27 2025 Areas affected...Central to Southern Appalachians Concerning...Heavy rainfall...Flash flooding possible Valid 272033Z - 280230Z Summary...Scattered pulse thunderstorms will develop through the evening across the Central and Southern Appalachians. Rainfall rates may briefly reach 3"/hr, producing short duration rainfall of 1-2". This could result in instances of flash flooding. Discussion...The GOES-E visible imagery this afternoon shows widespread convective development across the Appalachians. In general, these cells are discrete and scattered in a weakly forced environment, but local enhancement due to terrain features or storm mergers/outflow collisions have resulted in scattered clusters across the region as well. Thermodynamics today are favorable for heavy rainfall as PWs of 1.5 to 1.75 inches are collocated with SBCAPE of 2000-3000 J/kg. Forcing for ascent is generally provided via low-level upslope flow into the terrain and surface convergence along mergers/collisions, but weak diffluence aloft is also providing modest ascent in the area. Together, this ascent working into the favorable environment has produced radar-estimated rain rates of 1.5 to 2 inches per hour. The CAMs are in generally good agreement that scattered thunderstorms will continue to develop and move chaotically through loss of instability or convective overturning this evening. Mean 0-6km winds of just 5-10 kts combined with minimal bulk shear will provide a setup that supports primarily pulse convection with limited temporal duration. However, both the HREF and REFS ensembles indicate a moderate to high chance (50-70%) of at least 1"/hr rates leading to short-term rainfall as much as 1-2", and 15-min rainfall from the HRRR as much as 0.75" (brief 3"/hr rates). With storms expected to just drift across the area, any storm that occurs atop sensitive terrain or more urban areas could result in instances of flash flooding. While the threat is expected to be generally isolated, there is some potential in the next few hours of a more focused area of convection in KY and eastern TN. Here, pulse storms developing to the east will drift NW (along with outflows) and potentially merge with clusters coming out of the west. Some merging of these cells is shown, albeit with a lot of spatial spread, on the HRRR, NAM3km, and RRFS, which could briefly enhance the convection and accompanying heavy rainfall rate. Should this occur over some of the more sensitive soils (FFG as low as 1.5-2"/3hrs) it could cause a slightly higher risk for instances of flash flooding than the more isolated pulse type storms forecast across most of the area. Weiss ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!5i5gGy-GjUUQ_3mf5l7eCJCUSsq73Lp0t65-bkUqYqqbT4H_31ah0VArZtE9Ma0vKEPn= pTdpHPl5fO6pdtLYlmQDyg0$ for graphic product... ATTN...WFO...FFC...GSP...ILN...JKL...LMK...MRX...OHX...RLX... RNK... ATTN...RFC...ALR...ORN...TIR...NWC... LAT...LON 38768309 38568231 38268169 38058093 37368059=20 36588093 35798137 35338181 34908248 34538358=20 34528441 34818500 35458507 37038477 38368414=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) .