Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Sep 29 2024 22:51:32 AWUS01 KWNH 292251 FFGMPD MDZ000-VAZ000-WVZ000-300400- Mesoscale Precipitation Discussion 1082 NWS Weather Prediction Center College Park MD 651 PM EDT Sun Sep 29 2024 Areas affected...Central Appalachians Concerning...Heavy rainfall...Flash flooding possible Valid 292250Z - 300400Z Summary...Showers and thunderstorms are expected to increase in coverage and intensity during the next few hours. Rainfall rates within thunderstorms could reach 1-2"/hr, resulting in axes of 1-3" of rain with locally higher amounts. Flash flooding is possible. Discussion...The regional radar mosaic this evening indicates that convective coverage is finally beginning to expand and intensify across parts of Virginia. This is occurring in response to a slow rise in favorable thermodynamics noted by the SPC RAP analysis of SBCAPE reaching above 500 J/kg, coincident with PWs that are above the 90th climatological percentile at 1.6-1.8 inches. Into this overlapping moisture/instability, ascent is intensifying through height falls and divergence downstream of an upper low positioned over KY, topped by modest LFQ upper diffluence, and in the presence of 15 kts of 850mb inflow out of the SE. Not only is this inflow advecting the more robust thermodynamics northward into VA/WV, it is also increasing ascent through convergence along the nose of these higher wind speeds and through both isentropic and orographic response to this wind trajectory. Rainfall rates within the stronger convection have produced MRMS measured 1-hr rainfall over 1 inch in southern VA. Although the guidance has been a tad aggressive with convective intensity this aftn, likely due to a slower increase in favorable instability, the recent radar returns suggest this evolution is beginning. The convection over southern VA should continue to expand and then push N/NW on 0-6km winds that will gradually back from SW to S at 15-20 kts through the evening. This evolution is supported by most available high-res models, and despite the generally progressive motion of cells, repeating rounds are likely as storms regenerate into the stronger thermodynamics and pivot northward. The HREF neighborhood probabilities for 1"/hr (2"/hr) rain rates peak this evening above 60% (20%), greatest in the higher terrain where orographic lift will enhance the rainfall intensity. Where storms can regenerate and repeat, these rain rates could result in 1-3" of rain, with locally higher amounts possible as progged by 10-15% HREF/REFS neighborhood probabilities for 5"/6hrs. This area has been saturated with heavy rainfall that has been 3 to as much as 8 inches according to AHPS 7-day rainfall. This has led to compromised FFG and 0-10cm RSM from NASA SPoRT that is generally above 70%. Any heavy rain rates moving atop these sensitive soils could quickly become runoff leading to instances of flash flooding, but this appears most likely in the vulnerable terrain from the Blue Ridge through the Allegheny Mountains. Weiss ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!8Z26pDTsDC_CfmR6kII5vahQlRmluBqy0MaMUOFnwP0CYQBTTt4t8mZ2TGYj8lEUYn2B= BqWuIl_emAL9eJatlXBqRjU$ for graphic product... ATTN...WFO...AKQ...LWX...PBZ...RLX...RNK... ATTN...RFC...MARFC...OHRFC...SERFC...NWC... LAT...LON 39497924 39307868 38947824 38087791 37337793=20 36797818 36617867 36577921 36697990 37368065=20 37578109 38098128 39198033=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) .