Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Jul 24 2024 18:42:32 AWUS01 KWNH 241842 FFGMPD CAZ000-250040- Mesoscale Precipitation Discussion 0718 NWS Weather Prediction Center College Park MD 241 PM EDT Wed Jul 24 2024 Areas affected...Southern California Concerning...Heavy rainfall...Flash flooding possible Valid 241840Z - 250040Z SUMMARY...Showers and thunderstorms will be initiating and expanding in coverage over the higher terrain of southern California including portions of the San Bernadino and San Gabriel mountains and adjacent areas of the Peninsular Range. There will be concerns today for slow-moving and locally terrain-anchored convection that may produce heavy rainfall amounts and some flash flooding. DISCUSSION...GOES-W Day Cloud Phase RGB satellite imagery is showing the early stages of convective initiation taking place over the higher terrain of southern California and convection is expected to develop and locally expand in coverage over the next several hours as strong diurnal heating/boundary layer instability works in tandem with orographically enhanced differential heating boundaries and related mesoscale circulations. SBCAPE values have risen already to locally 1500 to 2500 J/kg, with areas east of the Peninsular Range including the interior deserts of southern CA seeing the greatest magnitudes currently. Much like areas farther north in the Sierra Nevada, the airmass is quite moist with CIRA-ALPW data showing a rather deep column of elevated moisture content, and the PWs are locally reaching 2+ standard deviations above normal. A combination of this moisture and instability near and adjacent to the terrain along with a favorable set-up for small-scale terrain-induced circulations should yield slow-moving pockets of showers and thunderstorms capable of producing heavy rainfall rates that may reach 1 to 2 inches/hour. The latest hires CAMs are very likely underdone with the rainfall potential, but some spotty 2 to 3 inch rainfall totals are generally expected where these slow-moving and locally focused pockets of convection set up. Isolated to widely scattered instances of flash flooding will be possible over the higher terrain of southern CA including the San Gabriel and San Bernadino mountains and the adjacent areas of the Peninsular Range. Some of the interior deserts where stronger instability is noted may also see some of this convection occur. Any burn scar locations in particular will be most susceptible to enhanced runoff concerns and flash flooding. Orrison ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!_16zA9SZMci7QWbB-CsXlc6yOSgIkhxbebOkT_c31U4wPTF_aeV5XmRbHOayZ8lYylos= OZIdjwV_qapyBJcIzotJSaE$ for graphic product... ATTN...WFO...HNX...LOX...PSR...SGX...VEF... ATTN...RFC...CNRFC...NWC... LAT...LON 35441712 35011640 33301548 32691556 32491608=20 32631658 33311703 33911783 34331886 34741928=20 34951908 34941810 35321766=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) .