Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Dec 21 2023 10:26:21 AWUS01 KWNH 211026 FFGMPD CAZ000-211530- Mesoscale Precipitation Discussion 1211...Corrected NWS Weather Prediction Center College Park MD 525 AM EST Thu Dec 21 2023 Corrected for minor grammatical errors within body of discussion Areas affected...southern Coastal into western Transverse Ranges Concerning...Heavy rainfall...Flash flooding likely Valid 210937Z - 211530Z Summary...Flash flooding will remain likely (although isolated) for the southern Coastal into the western Transverse Ranges of CA through 15Z. Peak hourly rainfall rates of 0.5 to over 1.0 in/hr can be expected. While these higher rainfall rates should remain localized, antecedent rainfall over the past 12-24 hours will factor into the potential for flash flooding. Discussion...09Z water vapor imagery showed a closed low centered offshore of CA near 33N 126W with a few well-defined vorticity maxima revolving around the center of the low. Infrared satellite and radar imagery have shown that what was once a north/south axis of higher intensity rainfall focused into Santa Barbara and Ventura counties, has pivoted, becoming aligned more NW to SE. A stronger cell within the axis of colder cloud tops was recently noted in southern Ventura County near Oxnard with a couple of reporting stations showing 1.5+ in/hr and over 1 inch of rain in 30 minutes, ending between 0900 and 0930Z. Support for these higher rates was coming from instability of 500 to 1000 J/kg MUCAPE located along and just offshore of the coastline via the 09Z SPC mesoanalysis page. Short term forecasts from the RAP support a continued southward movement to the closed low through 15Z with perhaps some slight eastward translation. This motion of the closed low will allow the low level moisture axis to become oriented a bit more from SE to NW, clipping coastal CA, including western Los Angeles, Ventura, Santa Barbara and southern San Luis Obispo counties. As the vorticity maximum located near 31.5N 125W (as of 09Z) advances closer to the coast, expectations are for 850-700 mb winds to increase 5-10 kt from their 09/10Z speeds (via RAP model), locally increasing IVT values into the coast. The southerly component of the low level moisture flux axis will continue to favor south-facing areas of terrain with the potential for peak rainfall rates of 0.5 to over 1.0 inches in an hour or less. Flash flooding will remain likely, but isolated, across a small portion of the southern Coastal into the western Transverse Ranges with an additional 1-2, locally 3+, inches of rain possible through 15Z. Otto ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!9NU_dohAWeJAvMGSApeRT7eX2atX_Dfl86Zx3VCLSOZ8AEsd8lt4ALnnksverZE-NVJo= D00Py9RUMR6bAU2wrmFDVWg$ for graphic product... ATTN...WFO...HNX...LOX... ATTN...RFC...CNRFC...NWC... LAT...LON 35352059 35072003 34811910 34581860 34061838=20 33821861 33721917 33872032 34192082 34922121=20 35302086=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) .