Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Dec 21 2023 04:10:12 AWUS01 KWNH 210409 FFGMPD CAZ000-210930- Mesoscale Precipitation Discussion 1210...Corrected NWS Weather Prediction Center College Park MD 1108 PM EST Wed Dec 20 2023 Corrected for typo in first paragraph Areas affected...southern CA Concerning...Heavy rainfall...Flash flooding likely Valid 210400Z - 210930Z SUMMARY...A nearly stationary axis of moisture transport will support training and repeating of showers/thunderstorms with rain rates peaking near 1 in/hr. Additional rainfall totals through 10Z of 1-2 inches along with local maxima near 3 inches are expected for portions of southern CA, which should support an increase threat for flash flooding. DISCUSSION...GOES West water vapor imagery at 0330Z showed an upper level closed low centered near 34N 126W, slowly drifting south. Several embedded vorticity maxima were noted to be revolving about the low center and upper level winds were widely diffluent along the south-central to southern CA coast. Infrared and regional radar imagery showed showers with embedded thunderstorms extending from the Channel Islands and northward from the south-central CA coast into the southern Santa Lucia and Diablo Ranges. Peak observed rainfall rates over the past few hours have been near 1 in/hr but these higher rates have been very localized within the western Transverse Ranges. Peak hourly rainfall over 0.5 in/hr has been noted elsewhere within the higher terrain across the region. An axis of IVT, peaking near 400 kg/m/s was located to the east of the closed low, focused across the Channel Islands into the western Transverse Ranges, fed by 25-35 kt of 850-700 mb layer winds along with precipitable water values near 1 inch along the coast. The upper low is forecast to continue a slow southward translation over the next 6 hours, with the associated axis of moisture transport remaining nearly stationary into the western Transverse Ranges. Weak MLCAPE of up to 500 J/kg just offshore of the southern CA coast may support thunder and higher intensity rainfall with potential for peak rates near 1 in/hr through training and repeating of cells. Given the favorable orthogonal orientation of the low level winds to the axis of terrain, the greatest potential for 1-2 and localized additional totals of 3 inches will be across southern San Luis Obisbo, Santa Barbara and Ventura counties through 10Z. Elsewhere, rainfall rates peaking near and just above 0.5 in/hr will be possible as far east as western San Bernardino and Riverside counties. Due to the slow movement of the axis of moisture transport, and continued rounds of heavy rain, combined with rainfall that has already occurred, the flash flood threat is expected to increase through the night with some localized but likely areas of flash flooding expected. The potential will be enhanced with overlap of heavy rain with sensitive burn scar regions. Otto ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!4O8JW-NrtgKYPaaEU-cAg072XIHbXiSPEzu3bn5CVfqMt71mT35VlyhY4nx7hVy06ic7= dRNv-hJsWeX1Ecy_GJfV5Dw$ for graphic product... ATTN...WFO...HNX...LOX...MTR...SGX... ATTN...RFC...CNRFC...NWC... LAT...LON 36672072 36402023 35911992 35361947 35041906=20 35091874 35061842 34711822 34501783 34501734=20 34281682 34071674 33691729 33551791 33541898=20 33872044 34362106 35092127 35882126 36422107=20 =20=20=20=20=20=20=20=20=20=20=20=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) .