Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Aug 19 2023 20:43:28 AWUS01 KWNH 192043 FFGMPD CAZ000-200241- Mesoscale Precipitation Discussion 0948 NWS Weather Prediction Center College Park MD 442 PM EDT Sat Aug 19 2023 Areas affected...Portions of the Central and Southern Sierra Nevada...San Joaquin Valley and the Transverse and Peninsular Ranges Concerning...Heavy rainfall...Flash flooding likely Valid 192041Z - 200241Z SUMMARY...An increase in slow-moving and locally terrain-anchored shower and thunderstorm activity is expected over the next several hours. Heavy rainfall rates are expected, and some isolated to widely scattered areas of flash flooding can be expected heading through the afternoon and early evening hours. DISCUSSION...GOES-W satellite imagery shows a mid and upper-level cloud deck arriving well ahead of Hurricane Hilary as it gradually approached the west side of the Baja Peninsula. This cloud deck has been helping to limit solar insolation to an extent, but sufficient heating in conjunction with an increase in the low and mid-level moisture transport ahead of Hilary has occurred to support spotty MUCAPE values of 1000+ J/kg across some of the low desert areas east of the Peninsular Range of southern CA and also farther north across southern portions of the San Joaquin Valley and near the foothills of the southern Sierra Nevada. Radar imagery has been showing some locally slow-moving convective cells developing and impacting portions of the southern Sierra Nevada and especially Inyo County and eastern Kern County over the last 1 to 2 hours and additional cell development is expected over the next several hours. Given the continued increase in boundary layer heating and instability overall, slow-moving convective cells are also likely to begin forming with strong aid of orographics/upslope flow over the eastern slopes of the Transverse Range and also the Peninsular Range including the San Gabriel, San Bernadino and San Jacinto mountains. PW anomalies over much of southern California increase to over 3 standard deviations above normal by 00Z as Hurricane Hilary continues to advance north-northwest. The instability and increasingly tropical nature of the vertical column coupled with orographic ascent should favor a rather high degree of rainfall efficiency. Some of the stronger storms may produce rainfall rates upwards of 1.5 to 2 inches/hour and this is supported by some of the latest experimental WoFS guidance which also suggests locally some storm totals of 2 to 3 inches where some of these slow-moving cells persist or become anchored near the higher terrain. Some instances of flash flooding will be likely as a result over the next several hours as convection tends to gradually develop and expand in coverage. This will include considerations of impacts to any burn scars and the dry washes away from the terrain over some of the lower deserts. Orrison ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!5dbzfk4-R3Iov-SF7BkHcWV9FsEJoqKWj3PhGTE-kecSKra-6lBPahFgyfLJlDQjZIib= _-A_O93y-9jaKQww3p5Lcxw$ for graphic product... ATTN...WFO...HNX...LOX...PSR...REV...SGX...VEF... ATTN...RFC...CNRFC...NWC... LAT...LON 37631891 37581821 36901753 35581696 34551618=20 33721573 32591576 32551676 33321717 34031803=20 34921900 35821956 36961955=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) .