Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Feb 24 2023 13:56:57 AWUS01 KWNH 241356 FFGMPD CAZ000-241955- Mesoscale Precipitation Discussion 0074 NWS Weather Prediction Center College Park MD 856 AM EST Fri Feb 24 2023 Areas affected...southern CA Concerning...Heavy rainfall...Flash flooding likely Valid 241355Z - 241955Z SUMMARY...Heavy rain coverage and intensity will expand across southern CA through the rest of the morning. Peak rainfall rates of 0.5 in/hr will increase above 0.8 in/hr through 20Z on a localized basis. Additional rainfall of 2-4 inches over the next 6 hours is expected to increase the threat for flooding in the metro locations and areas of terrain below snow levels. DISCUSSION...GOES West water vapor imagery at 13Z showed a strong closed low dropping southward off of the northern coast of CA with the 12Z RAOB network sampling a 110 to 120 kt upper level jet from VBG to VEF located southeast of the upper low center. Blended TPW imagery depicted a broad shield of subtropical moisture advancing toward the CA coast ahead of an occluded/cold front with values over 0.8 inches along 30N and as far east as 123W. Areas of heavy rain are ongoing from San Luis Obispo into Santa Barbara counties with observed rainfall totals over 0.5 in/hr. The closed low is forecast to continue advancing southward over the next six hours which should support the continued transport of moisture into the southern CA coast with precipitable water values rising to over 0.8 inches by ~20Z. 850 mb winds of 30 to 50 kt oriented SSW or perpendicular to the Transverse Ranges will promote an ideal upslope component and orographic enhancement to rainfall intensity. As the upper low advances south, mid-upper level diffluence will increase along with some enhancement within the right entrance region of the aforementioned upper level jet max, supporting an expansion/increase of heavy rain from the coast into the mountains. Snow levels are unusually low for this time of year but will rise somewhat from current levels into the 5000-6000 ft range by early afternoon per recent NAM forecasts. Flooding impacts are likely to increase over the next 3-6 hours, especially with any exposed burn scar locations below snow levels and in other areas of poor drainage. Peak additional rainfall totals through 20Z are expected to range from 2-4 inches. Otto ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!97st3xbAuBf1Q_i6S7iKxlt9svO0GmfW3qOqcWZBFjX5OXSYkXo7akJYQekBk37zDcwF= sDfLwZG1rgCCw1vjwPdpUKs$ for graphic product... ATTN...WFO...LOX...SGX... ATTN...RFC...CNRFC...NWC... LAT...LON 35142057 34962018 34721981 34641960 34571940=20 34581904 34591879 34781895 34671852 34601827=20 34521826 34431829 34341812 34271807 34251794=20 34291779 34221758 34251741 34141738 33671755=20 33291823 33111888 33191950 33542010 34092060=20 34852105=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) .