Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Jun 09 2025 23:23:28 AWUS01 KWNH 092323 FFGMPD NYZ000-PAZ000-MDZ000-VAZ000-WVZ000-100520- Mesoscale Precipitation Discussion 0413 NWS Weather Prediction Center College Park MD 723 PM EDT Mon Jun 09 2025 Areas affected...Portions of the Lower Great Lakes and Central Appalachians Concerning...Heavy rainfall...Flash flooding likely Valid 092320Z - 100520Z SUMMARY...Ongoing thunderstorm activity ahead of an advancing cold front is expected to continue exhibiting brief training and likely producing additional isolated to scattered instances of flash flooding into at least the early overnight period. Maximum hourly amounts of 1-1.5" are most likely, but should occur within the very saturated and already flood-prone region of the central Appalachians. DISCUSSION...Latest radar, satellite, and surface observations indicate periods of heavy rainfall and numerous thunderstorms stretching from northwest PA into western NY, along with developing cells and scattered thunderstorms across central PA into WV and northern VA. These storms are all generally moving northeastward ahead of an approaching pair of cold fronts swinging across the Great Lakes. Meanwhile, easterly low-level flow off the Atlantic has produced an area of convergence along the central Appalachians extending from western VA along the Allegheny Mts through Upstate NY. This area of convergence could be a focus along sensitive terrain (1-hr FFG less than 1") for brief training/slow-moving storms and scattered flash flooding. PWs in the area are generally around 1.3-1.5", which isn't too spectacular and falls under the 90th climatological percentiles per the NAEFS ESAT. However, the strong southwesterly 850mb flow of 35-40 kts increase IVT above the 90th climatological percentile and could be what pushes the setup towards greater flash flooding potential for a few additional hours after sunset. Instability remains sufficient along this convergence zone with MLCAPE over 1,000 J/kg, leading to the maintenance of updrafts due to the combined effective bulk shear in the area. Latest HRRR and experimental RRFS guidance depicts hourly totals up to 2" possible and 18z HREF probabilities for 3-hr totals greater than 2" as high as 40%. All of this within a region of the central Appalachians containing 1-hr FFG less than 1" and 3-hr FFG less than 2", as well as monthly rainfall running 200-300% above normal. These factors support the likelihood of additional isolated to scattered flash flooding, but with the magnitude of impacts potentially limited given the overall storm system is progressing eastward with time. Snell ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!5ThDQOe09jaiTiQ6WW3f6kzi2MOJvymk3fwPZ9k3lUC3mfTpZJirPre-3Os14FUKM2cM= DgZHl-p60loNrU8b5228ZeM$ for graphic product... ATTN...WFO...BGM...BUF...CTP...LWX...PBZ... ATTN...RFC...RHA...TAR...TIR...NWC... LAT...LON 44037585 43387535 41367669 39817749 39077824=20 39127926 39677983 41007947 42567801 43737661=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) .