Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Aug 21 2023 00:14:52 AWUS01 KWNH 210014 FFGMPD NVZ000-CAZ000-210613- Mesoscale Precipitation Discussion 0955 NWS Weather Prediction Center College Park MD 814 PM EDT Sun Aug 20 2023 Areas affected...Southern CA...Southern NV Concerning...Heavy rainfall...Flash flooding likely Valid 210013Z - 210613Z SUMMARY...Life-threatening and locally catastropic flash flooding is expected this evening across large areas of southern California as Tropical Storm Hilary advances north and brings and produces very heavy rainfall totals. Meanwhile, heavy rains and flash flooding concerns will be increasing over southern Nevada. DISCUSSION...The late-day GOES-W 1-minute IR and visible satellite imagery in conjunction with surface and radar observations shows the center of weakening Tropical Storm Hilary lifting steadily north across southern CA. As of 5PM PDT (00Z), the center of Tropical Storm Hilary was centered 25 miles south-southwest of Palm Springs, CA with the storm moving north at 23 mph. Hilary continues to bring very heavy rainfall across southern CA with very strong moisture transport and enhanced orographic forcing/upslope flow working to maintain locally enhanced rainfall rates that are occasionally reaching 1 to 1.5 inches/hour. Some of this is being aided by the uptick seen over the last few hours of boundary layer instability over southeast CA including the Mohave and Colarado Deserts where MUCAPE values have risen to as high as 1000 to 2000 J/kg. Strongly convergent southeast flow around the eastern flank of Hilary coupled with the instability will result in some banded convective structures heading through the evening hours impacting portions of the Mohave Desert and also the upslope areas of the southern Sierra Nevada. Meanwhile, some of the remaining central convection and core of Hilary's rains will be concentrated over the Transverse Range and southern portions of the San Joaquin Valley, with this activity also crossing through the southern Sierra Nevada over the next several hours. Already there has been locally as much as 2 to 4 inches of rain across some of the east and northeast facing slopes of the San Gabriel and San Bernadino mountains of the Transverse Range in just the last 6 hours, with storm totals amounts going back to early this morning that are approaching 6 inches. The 18Z HREF guidance along with recent runs of the HRRR and the experimental WoFS guidance all generally show the 00Z to 06Z time frame as generally being the window of the heaviest rains for Hilary across southern CA with the heaviest amounts expected generally over the San Gabriel and San Bernadino mountains, and to a slightly lesser extent the southern Sierra Nevada where additional rainfall amounts of 2 to 4 inches with isolated 5+ inch amounts will be possible going through 06Z (11PM PDT). Expect these rains to also be reaching over somewhat into the Nevada side of the Sierra Nevada crest. These rains will result in life-threatening and locally catastrophic flash flooding impacts including debris flows, landslides and mudslides going through the evening hours. Orrison ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!7b4gZlGtHVxQZs_kGkyGXNon_XBA0mlHdZMofdqC0aP9cATfqsCb49IIfYgGeuXkeS2t= MF4toJizQTIMO-NrCDEFkcY$ for graphic product... ATTN...WFO...HNX...LKN...LOX...PSR...REV...SGX...VEF... ATTN...RFC...CBRFC...CNRFC...NWC... LAT...LON 38101720 37641652 36301559 34891511 33631515=20 32591605 32551688 32791734 33531785 33721870=20 34411929 35301938 36601867 37801817=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) .