Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Sep 10 2023 21:00:39 AWUS01 KWNH 102100 FFGMPD PAZ000-MDZ000-VAZ000-NCZ000-WVZ000-TNZ000-KYZ000-110200- Mesoscale Precipitation Discussion 1054 NWS Weather Prediction Center College Park MD 459 PM EDT Sun Sep 10 2023 Areas affected...Appalachians from northwest NC through western MD Concerning...Heavy rainfall...Flash flooding possible Valid 102058Z - 110200Z Summary...Showers and thunderstorms will persist into this evening with rain rates exceeding 1"/hr at times. These storms will be slow moving, and bring an additional 1-2" of rain with locally higher amounts atop pre-saturated soils. Flash flooding is possible. Discussion...The regional radar mosaic this afternoon shows an axis of moderate rain with embedded thunderstorms from far SW VA through the southern Laurel Highlands. Additional showers and thunderstorms are also developing across NW NC. This activity is blossoming in response to a 500mb trough which is slowly advecting eastward, resulting in modest height falls collocated with the RRQ of a jet streak to the north. This ascent is also being enhanced by a weak shortwave noted in WV imagery shifting northeast into WV, while modest convergence between 850-700mb occurs along an axis downstream of the primary longwave trough. Together these are resulting in plenty of deep layer ascent atop favorable thermodynamics characterized by PWs of around 1.5 inches and SBCAPE of 1500 J/kg, to result in radar-estimated rain rates of 1-1.5"/hr. Although instability may struggle to improve due to widespread cloud cover and, in some places, an already worked-over environment, the robust ascent and moist column will still support scattered convection with heavy rainfall through the evening. The HREF and RRFS TL ensembles suggest the heaviest rainfall will occur in the next 2-4 hours, and should be focused downstream of the shortwave and along the aforementioned 850-700mb convergence axis. Here, rainfall rates have a 50-70% chance of exceeding 1"/hr according to the HREF, which through the slow motions have a 20-40% chance of producing 3" of rainfall. While the overall coverage of the most intense convection may be somewhat muted the rest of today, the antecedent soils are primed for rapid runoff leading to flash flooding. 40cm soil moisture from NASA SPoRT is above the 95th percentile in many areas of the central/southern Appalachians from recent rainfall, leading to compromised FFG as low as 1-1.5"/3hrs. The HREF FFG exceedance probabilities peak only around 30-40% in the next few hours, but considering the vulnerability of these soils, especially in sensitive terrain features, suggests at least an isolated flash flood threat will continue into this evening. Weiss ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!56plNJIsOUO69Cs9AVez3mRRLMV2xLs1gnlzECW-N_w7CnXsUhYzCqDQbn2OnnulGou8= UCu1UcwD59pZiSEraZTWPpc$ for graphic product... ATTN...WFO...CTP...GSP...JKL...LWX...MRX...PBZ...RLX...RNK... ATTN...RFC...LMRFC...MARFC...OHRFC...SERFC...NWC... LAT...LON 39897929 39697825 38947811 38067864 37497932=20 36918007 36438053 36378061 35928133 35838177=20 35868217 36008261 36238289 36838270 38248172=20 39498062=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 3.14-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .