Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Aug 21 2023 06:06:58 AWUS01 KWNH 210606 FFGMPD AZZ000-NVZ000-CAZ000-211200- Mesoscale Precipitation Discussion 0956 NWS Weather Prediction Center College Park MD 206 AM EDT Mon Aug 21 2023 Areas affected...portions of Southern and Central CA...much of NV Concerning...Heavy rainfall...Flash flooding likely Valid 210600Z - 211200Z Summary...Numerous to widespread flash floods to continue in association with anomalous moisture from Tropical Storm Hilary. Localized rainfall rates of 0.5-1.0"/hr will generally persist, but may occasionally reach as high as 1-2"/hr. Additional totals of 2-4" are possible in association with topographic lift. Discussion...The near-surface circulation of Tropical Storm Hilary continues to become more ill-defined as it moves farther inland at this late hour, but heavy rainfall in association with the storm continues. Flash floods remain numerous to widespread across much of Southern California, with some localized catastrophic flash flooding likely still ongoing across the Transverse Ranges and northward into the High Desert and along the eastern and southern slopes of the southern Sierra Nevada and Inyo Mountains (including Death Valley). These flood impacts are expected to continue for at least a few more hours along the Transverse Ranges (i.e. San Bernardino and San Gabriel Mountains and surroundings), with the potential for additional localized totals of 2-4" through 12z (per the 00z HREF and subsequent HRRR guidance). Similar totals are expected in the vicinity of elevated terrain across east-central CA and into the south-central NV ranges, as moderate to strong southerly low-level moisture transport continues into this region. With forecast 6-hr precipitation of these magnitudes into the High Desert and Great Basin, the probabilities for 100 year average recurrence interval (ARI) exceedance are quite high (40-90% per 40-km neighborhood HREF guidance, given that these 100 year ARI thresholds are generally 1.0-2.0". As a result, locations that do not normally experience flooding are expected to realize scattered to numerous instances of flash flooding in association with highly anomalous moisture from decaying Tropical Storm Hilary. Washes that are normally dry, burn scars, and other low-lying/poor drainage areas are anticipated to see the most significant to potentially life-threatening flash flooding, along with lingering flooding impacts across the Transverse Ranges and Low Deserts (including Coachella Valley and Greater Palm Springs). Localized hourly rates may occasionally reach as high as 1-2" in association with enhanced topographic lift/upslope flow, but will more generally range from 0.5-1.0". Churchill ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!8HSPHB9VSwXezFy1fJ5HgklbGOAUfMLHo2RgAPljjhMYWVLqxQam30JNUfIdF-P-vwAs= q4UWHEG-qavQ_lwguVsyZkc$ for graphic product... ATTN...WFO...HNX...LKN...LOX...PSR...REV...SGX...STO...VEF... ATTN...RFC...CBRFC...CNRFC...NWC... LAT...LON 39701808 39501713 39341628 39261542 38921508=20 37871472 37281450 36421445 35281442 34861504=20 33331525 33161623 33091687 33211760 33501818=20 33921931 35021949 36061967 36822000 37672034=20 38592054 39072028 38991903=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) .