Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Mar 10 2023 06:41:01 AWUS01 KWNH 100640 FFGMPD NVZ000-CAZ000-101800- Mesoscale Precipitation Discussion 0093 NWS Weather Prediction Center College Park MD 140 AM EST Fri Mar 10 2023 Areas affected...much of California Concerning...Heavy rainfall...Flash flooding likely Valid 100600Z - 101800Z Summary...A landfalling atmospheric river is expected to continue spreading heavy rainfall across most of California through 18Z Friday. Widespread areas of 1 inch rainfall totals are expected, though terrain-favored upslope areas are expected to experience 2-5 inches of rainfall that could result in widespread, rapid onset flooding especially where rainfall induces melting of snowpack. Discussion...An ongoing, landfalling atmospheric river continues to produce widespread rainfall across many areas of the state currently. Environmental conditions supporting this landfalling atmospheric river include 1) a gradually moistening airmass, with 1.3.1.5 inch PW values now approaching central coastal areas of California and 2) gradually increasing low- to mid-level west-southwesterly flow against the terrain - now exceeding 50 knots at 850mb in several places. The combination of moisture and upslope was resulting in mainly light rainfall over the discussion area so far, with hourly rain rates of 0.1-0.25 inch/hr in most areas. Higher rainfall rates were estimated where terrain influences were more pronounced (exceeding 0.25 inch/hr along upslope areas of the Sierra and along localized areas of central California coastal ranges per MRMS and observations). The ongoing regime should continue through 18Z and beyond. Models indicate that an uptick in precipitation rates and totals are likely through that time frame - especially in aforementioned areas of enhanced upslope as wind fields remain strong (or even increase slightly) and moisture continues to increase. Heaviest rainfall totals (ranging from 2-5 inches) are likely along upslope regions of the southern Sierra and along central California coastal ranges generally extending from Santa Barbara to Monterrey. These areas will also be aligned well with maximum Integrate Water Vapor transport (exceeding 800 kg/m*s) through the 18Z. Of particular concern is the existence of this heavy rainfall on snowpack along upslope regions of the Sierra. As snow levels rise into the 8000-10000 foot range, rainfall on snowpack should result in areas of increased runoff and rapid onset of flooding.=20 Additionally, areas of modest instability along coastal areas could combine with terrain influences to boost rainfall rates into the 0.5-1.25 inch/hr range at times. Each of these scenarios could contribute to significant, widespread flooding at times today. Cook ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!7n3iB2JiZSLPXpV1eJVcG7OmLO3GUzg6yLlao4qO-hV-FjSfNe7DkoYnf6ZbYJkpcJPA= UqAugsZdyermW5uS7GIj2Eg$ for graphic product... ATTN...WFO...EKA...HNX...LOX...MFR...MTR...REV...SGX...STO... VEF... ATTN...RFC...CNRFC...NWC... LAT...LON 41572431 41512339 40572229 40302100 39612002=20 38771941 37801838 36801753 35451687 34791706=20 34501803 34331977 34582102 36012182 37402282=20 38502356 39972450 40742474=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) .