Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Jul 22 2024 02:18:34 AWUS01 KWNH 220218 FFGMPD VAZ000-NCZ000-SCZ000-GAZ000-TNZ000-220600- Mesoscale Precipitation Discussion 0687 NWS Weather Prediction Center College Park MD 1017 PM EDT Sun Jul 21 2024 Areas affected...Southern Appalachians Concerning...Heavy rainfall...Flash flooding possible Valid 220217Z - 220600Z Summary...Scattered showers and thunderstorms will continue to develop and move slowly across the Southern Appalachians. Rainfall rates of 2-3"+/hr, will produce pockets of 2-4" of rain. This may lead to flash flooding. Discussion...The regional radar mosaic this evening shows continued development of slow moving thunderstorms from northern Georgia, across the Blue Ridge Mountains of NC, and into far southwest VA. This convection is blossoming within favorable thermodynamics characterized by PWs of 1.8 to 2.0 inches, and pronounced MUCAPE of 1000-1500 J/kg. The 00Z U/A soundings at KFFC and KRNK both depict a deeply saturated column with moist adiabatic lapse rates of 6C/km through around 400mb, and freezing levels of 12,000-14,000 ft, indicating the likelihood of continued efficient warm collision rain processes. Forcing for ascent is being provided through subtle PVA downstream of a shortwave lifting out of Alabama, weak diffluence in the tail of a modest jet streak aloft, and some locally backed 850mb winds lifting moisture northward into a front and more orthogonally into terrain features. Together this is producing convection with radar-estimated rainfall rates of 2-2.5"/hr, with slow motions at times due to terrain influences. The CAM signal the next several hours is in good agreement that scattered thunderstorms will continue to develop, especially east of the NC/TN border thanks to more impressive upslope enhancement. Moisture will remain considerable to support heavy rain rates, and both the HREF and REFS indicate a 20-40% chance of 2"/hr rates, with HRRR 15-min accumulations of 0.75" or more possible suggesting briefly even higher rates. The best chance of additional slow moving storms to cause flash flooding will be in the next 3-4 hours as 850mb flow remains subtly backed to converge along its nose and into the terrain, but the guidance agrees that overnight the flow will veer to become more uniformly SW. This will continue a training risk, but the thermodynamic transport should weaken at this time, as will the low-level convergence. Until that occurs, the heavy rain producing storms could cause pockets of 2-4" of rainfall. This area has been wet recently noted by AHPS 7-day rainfall of 150-300% of normal, which has saturated soils and lowered FFG to 1-1.5"/1hr and 1.5-2.5"/3hrs. These saturated soils indicate that any heavy rainfall could quickly become runoff, and where this occurs over sensitive terrain it could result in instances of flash flooding. Weiss ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!69Q_6UyqN0fPFMRfwttGc33iPlyvUqgT9Hl-Xd2BICKsEKYn1XOU7IwGzgq9cSEcBN4L= GGkOmYnowGCqNNo4Zm6gyf0$ for graphic product... ATTN...WFO...FFC...GSP...MRX...RNK... ATTN...RFC...LMRFC...OHRFC...SERFC...NWC... LAT...LON 36678176 36638109 36418060 36108090 35768125=20 35408186 34928243 34498296 34258343 34208388=20 34198431 34258480 34458504 34798507 35078484=20 35438455 35868408 36088355 36308296 36548254=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) .