Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Jan 07 2023 06:37:34 AWUS01 KWNH 070637 FFGMPD CAZ000-ORZ000-071700- Mesoscale Precipitation Discussion 0025...Corrected NWS Weather Prediction Center College Park MD 137 AM EST Sat Jan 07 2023 Corrected for typo in 1st sentence of discussion section Areas affected...northwestern CA into southwestern OR Concerning...Heavy rainfall Valid 070500Z - 071700Z Summary...Locally heavy rain is expected for the favored south/southwest facing terrain from the northern CA coast into southwestern OR. Hourly rainfall totals may approach 0.5 in/hr and 12-hr rainfall totals of 1-2, locally as high as 3 inches are expected through 17Z. Discussion...GOES West water vapor and 10.3 micron imagery at 04Z showed a pair of vorticity maxima (39N 129W and 39N 132W) located within the base of a mid-upper level trough, located off of the West Coast. Downstream of the eastern-most vorticity max was an area of cooling cloud tops approaching the northern CA and southern OR coastline. Ridging observed over the Great Basin has slowed the eastward translation of the larger scale trough axis over the eastern Pacific and local radar imagery from KBHX showed an area of perceived moderate to heavy rain repeating offshore from south to north, about 10-30 miles west of Cape Mendocino, CA. The delayed eastward push has been observed through trends in recent HRRR cycles showing a westward trend in heavy rain offshore of the West Coast through 12Z. The approach of the shortwave trough located between the two vorticity maxima is expected to support the development of a surface low along the front roughly 250 miles west of San Francisco near 06Z, with forecast movement toward the northeast, but remaining offshore. Nearly due southerly 850 mb winds of 50-60 kt are expected to set up along the northern CA/southern OR coast along with precipitable water values of 0.7 to 0.9 inches. A developing 70-90 kt jet steak at 250 mb, downstream of the shortwave trough, is forecast by recent runs of the RAP to focus divergence aloft along the CA/OR border along with a broader region of increasing diffluence, helping to increase rainfall coverage and intensity. The result will be areas of heavy rain eventually making it ashore with peak hourly totals approaching 0.5 in/hr. The timing of the heaviest rain appears to begin near 12Z and focus mostly from Humboldt to northern Sonoma counties. Peak rainfall over the next 12 hours is expected to mostly range from 1-2 inches but with localized maxima near 3 inches through 17Z. Given wet antecedent conditions and area burn scars, localized flooding cannot be ruled out. Otto ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!-4A0vA_vqcpPUOUG8zgZ4blBYvXzTlq4g4DxJ9w65jlWFDOQxGrAvUmSJESyAlLQLKb3= L9_RXeYXhQ_lsU5SRhqLzO0$ for graphic product... ATTN...WFO...EKA...MFR...MTR...STO... ATTN...RFC...CNRFC...NWRFC...NWC... LAT...LON 43232435 43002398 42442380 41592372 41132327=20 41282262 41222220 40882214 40612260 40062292=20 39022292 38462322 38482381 39322435 40672473=20 42292491 43092470=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) .