Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Aug 18 2023 23:02:38 AWUS01 KWNH 182302 FFGMPD AZZ000-NVZ000-CAZ000-190500- Mesoscale Precipitation Discussion 0944 NWS Weather Prediction Center College Park MD 700 PM EDT Fri Aug 18 2023 Areas affected...Far Southern NV...Southeast CA...Western and Southern AZ Concerning...Heavy rainfall...Flash flooding likely Valid 182300Z - 190500Z SUMMARY...Showers and thunderstorms are expected to increase further in coverage over the next several hours. Isolated to widely scattered instances of flash flooding are likely. DISCUSSION...The late-afternoon GOES-W satellite imagery in conjunction with dual-pol radar shows scattered areas of showers and thunderstorms impacting areas of southern NV, southeast CA and western and southern AZ. The airmass across this region is quite unstable with MLCAPE values as high 1500+ J/kg with the aid of strong boundary layer heating and a very moist airmass courtesy of a deep layer monsoonal moisture transport regime. Some additional expansion of shower and thunderstorm activity is expected for the remainder of the afternoon and at least the early to mid-evening hours as the ongoing convection facilitates mesoscale outflow boundary interactions/collisions with subsequent development also aided locally by orographics while embedded within the very moist and unstable airmass pooled over the region. Some weak but increasing upper-level support will be noted as well as many areas of western and southern AZ and also southeast CA will be gradually coming under the influence of diffluent flow aloft in between the anticyclonic outflow extending north of Hurricane Hilary south of Baja California and also the upper low/trough just offshore of the West Coast. This along with the persistent poleward advance of moisture from the Gulf of Calfornia and northwest Mexico will favor a threat of convective sustenance going well into the evening hours. Some rainfall rates will likely reach or potentially even exceed 2 inches/hour with the stronger storms heading into the evening hours. Experimental 00Z/18 MPAS-HN and MPAS-HT CAMs from NSSL along with the 12Z/18 HREF FV3-LAM solution all seem to have a fairly decent handle of the ongoing activity, and also suggest some localized upscale growth of convection with heavy rainfall amounts that may reach as high as 2 to 4 inches where some potential cell-merger activity occurs along with instances of very slow cell-motions. The additional rainfall threat this evening will likely drive isolated to widely scattered instances of flash flooding, and the normally dry washes across the region in particular will be vulnerable to enhanced runoff concerns. Orrison ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!9cDh92X-OClanyjtsBtioULohkEGUqbUt-e0ywBDpCdC-xcQkPGYtiaNeefK6YhAn721= hFOnHqY-0QMYiLFv1OI4meI$ for graphic product... ATTN...WFO...FGZ...PSR...TWC...VEF... ATTN...RFC...CBRFC...CNRFC...NWC... LAT...LON 36631463 35971319 34991234 34161073 33240949=20 32340925 31420962 31291103 31551211 32001371=20 32911510 34281589 36231592=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) .