Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Feb 01 2025 19:17:41 AWUS01 KWNH 011917 FFGMPD CAZ000-020700- Mesoscale Precipitation Discussion 0011 NWS Weather Prediction Center College Park MD 217 PM EST Sat Feb 01 2025 Areas affected...central to northern California Concerning...Heavy rainfall Valid 011915Z - 020700Z SUMMARY...Heavy rain will develop across north-central CA this afternoon and especially tonight. Rainfall will be steady but with hourly totals increasing to over 0.5 inches, especially for the northern Sierra Nevada tonight. 12 hour totals of 3 to 6+ inches can be expected for the northern Sierra Nevada with 1 to 3 inches for the Coastal Ranges. DISCUSSION...A big picture view of Blended Total Precipitable Water (PW) and MIMIC Total PW showed a southwest to northeast oriented axis of PW values in excess of 1.5 inches streaming across HI to about 36N, and extending east to about 127W, weakening with eastward extent to the West Coast. Land-based GPS data from 18Z showed that PW values of greater than 1 inch extended from northern Mendocino County to Santa Barbara County with a max near 1.25 inches centered around San Francisco Bay and eastward into the lower Sacramento River Valley. The values within the core of the moisture axis are well over 200 percent of normal via the blended imagery. Placement of a low ot mid-level low over British Columbia and ridge centered about 600 miles west of the northern Baja Peninsula has allowed for a funneling of these anomalous moisture values into the CA coast. A powerful (191 kt at 250mb via 12Z SLE sounding) zonally oriented upper level jet was sandwiched between the low to the north and high to the south, with no significant movement of these two features forecast through early tonight. Recent GFS, RAP and other guidance are good agreement with the arrival of a corridor of stronger 850 mb winds (40-50 kt) arriving into Sonoma and Marin counties over the next 1-2 hours, oriented perpendicular to the coastline along and just south of a east-west oriented quasi-stationary front extending offshore of the central CA coast. Some backing of low level flow toward the southwest is expected across the Valley into the foothills of the Sierra Nevada. With the increase in low level flow and a subtle increase in PW values (up to ~1.4 inches), IVT magnitude is expected to peak between 800-900 kg/m/s from just north of San Francisco Bay into the southern Sacramento Valley in the 21Z-02Z time frame. The surge will be short-lived however and poor low and mid level lapse rates should limit instability to near zero for coastal and inland locations through the first half of tonight with rainfall intensity largely driven by wind speed and orographic lift. Steady light to moderate rain was ongoing across the coast and Sierra Nevada of north-central CA as of 18Z but should increase in magnitude over the next 6 hours, especially into the upslope regions of the Sierra Nevada where orographic ascent will be maximized given 700 mb winds peaking in the 70-80 kt range just after 00Z. 12 hour rainfall totals of 1 to 3 inches are expected for the Coastal Ranges from just north of San Francisco Bay to just south of 40N and 3 to 6+ inches for the Sierra Nevada from roughly Amador to Butte counties. While rainfall through 07Z is not expected to produce impacts from flooding, heavy rain will continue through the night with potential for flooding and higher rain rates to increase prior to 12Z. Otto ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!5dIiGAeulu1rxK0zydcPEuCyMtNZXnx8os26hae-z-rkAXFPgV4aUFw3fciXn_7RGhfq= v6P58ylRb53IJTNahh-6NHU$ for graphic product... ATTN...WFO...EKA...HNX...MTR...REV...STO... ATTN...RFC...CNRFC...NWC... LAT...LON 40442163 40302137 40112102 39882047 39442017=20 38772012 38181972 37901960 37541946 37371955=20 37521991 37722010 38022037 38332090 38262158=20 37982207 37892261 37972305 38372341 38722374=20 39002387 39362397 39652383 40062346 40262297=20 40412231=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 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .