Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Aug 07 2024 17:08:26 AWUS01 KWNH 071708 FFGMPD NJZ000-PAZ000-DEZ000-MDZ000-VAZ000-DCZ000-WVZ000-072300- Mesoscale Precipitation Discussion 0827 NWS Weather Prediction Center College Park MD 107 PM EDT Wed Aug 07 2024 Areas affected...Portions of WV eastward through DE and southern NJ Concerning...Heavy rainfall...Flash flooding possible Valid 071706Z - 072300Z Summary...Showers and thunderstorms will expand across portions of the Mid-Atlantic through this evening. Rainfall rates of 1-2+"/hr rates are likely, which through slow storm motion could produce 2-3" of rain with locally higher amounts around 5" possible. This could cause instances of flash flooding. Discussion...The regional radar mosaic this afternoon shows rapid expansion of reflectivity associated with developing showers and thunderstorms from WV into northern VA and across eastern MD/DE. These storms are firing along a west-to-east oriented stationary front analyzed from WV to southern NJ, providing low-level convergence for ascent. This boundary is additionally being acted upon by a weak impulse noted in WV imagery moving across southern PA and from upper diffluence in the RRQ of a jet streak arcing into New England. Thermodynamics across the region are favorable for heavy rain with PWs measured by GPS of 1.7-1.9 inches, close to the KLWX 12Z U/A sounding which measured 1.83 inches, right at the 90th percentile according to the SPC sounding climatology, overlapped with pocket of MLCAPE exceeding 1000 J/kg. During the next few hours, convection should become increasingly widespread and intense as SBCAPE climbs towards 2000 J/kg and PWs surge above 2 inches as tropical moisture begins to stream northward from T.S. Debby to the south. With the synoptic forcing mechanisms remaining into this impressive thermodynamic environment, there is strong support for widespread coverage of showers and thunderstorms which is reflected by CAMs simulated reflectivity. There may be two areas of higher coverage, one over eastern MD into DE, and a second across the terrain of WV and western MD, but convective development is possible anywhere within the discussion region. Storms that develop have a high chance (60-80%) of 1"/hr rates, and may at times reach 2-3"/hr as suggested both by HREF neighborhood probabilities and the HRRR 15-min rainfall accumulation product. Mean 0-6km winds will remain light through the aftn, just 5-10 kts, and feature a variety of motions due to varying winds and weak shear. This could result in storm interactions to briefly enhance rain rates even further, while also leading to total rainfall of 2-3" with locally higher amounts nearing 5" as shown by HREF 5"/6hr neighborhood probabilities reaching 20-30% in eastern MD, lower elsewhere. 7-day rainfall across the region according to AHPS has been 100-300% of normal across much of MD, but the areas expected to receive the most rainfall today have also been drier during this period. This is reflected by generally below normal 0-40cm soil moisture according to NASA SPoRT, and FFG that is as much as 3"/3hrs outside of terrain or urban influences. HREF exceedance probabilities peak only around 20%, but the slow motion of any intense rain rates could still cause instances of rapid runoff leading to flash flooding. Weiss ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!_C90JtQRJIv4JV7NluuTUgpF2J8Llam-2FgB0xUFrb5cV5z96HNuQhLaa-JfBTG-tMu8= 6smlnoTv1y_WCms4ilnCzYg$ for graphic product... ATTN...WFO...AKQ...CTP...LWX...PBZ...PHI...RLX... ATTN...RFC...MARFC...OHRFC...NWC... LAT...LON 39997553 39977542 39617435 39327404 39067414=20 38487455 38157527 37917583 37717633 37567678=20 37467730 37367754 37677817 38097885 38327961=20 38328026 38298074 38608104 39118094 39657988=20 39737926 39627877 39677760 39867669=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) .