Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Dec 27 2022 08:02:41 AWUS01 KWNH 270802 FFGMPD CAZ000-ORZ000-271800- Mesoscale Precipitation Discussion 1173 NWS Weather Prediction Center College Park MD 300 AM EST Tue Dec 27 2022 Areas affected...Far Southwest OR...Northern/Central CA Concerning...Heavy rainfall...Flash flooding possible Valid 270800Z - 271800Z SUMMARY...Robust atmospheric river conditions continue to gradually settle south down the West Coast. Heavy rains to continue this morning across the coastal ranges and into the foothills of the Sierra Nevada. Areas of flooding will be possible, including a threat of some flash flooding and debris flow activity near any burn scar locations. DISCUSSION...A strong upper-level trough and associated surface low offshore of the West Coast continues to move east toward the Pacific Northwest while driving a strong atmospheric river inland across the region. Satellite and radar imagery shows heavy rain impacting many areas of southwest OR and down through northern CA with an emphasis on the coastal ranges and also the foothills of the northern Sierra Nevada. Meanwhile, surface observations in conjunction with satellite data show a cold front just beginning to push inland. The IVT values with this atmospheric river event are just past peak across areas of southwest OR and northwest CA for the event, but remain high, as a trans-Pacific fetch of deep moisture with some subtropical origins (per CIRA-ALPW data) remains in place. This axis of enhanced moisture transport will be gradually shifting farther south down the coast as the offshore cold front moves farther inland. The 00Z NAM/GFS solutions show a ribbon of 800 to 1200 kg/m/s IVT values impacting the northern CA coastal ranges for a few more hours, with the nose of this losing latitude and weakening this morning to an order of 600 to 800 kg/ms/s by 18Z across central CA, with lesser values farther inland making it into the foothills of the Sierra Nevada. Regardless of the weakening IVT trends with time, strong warm air advection ahead of the cold front along with a largely orthogonal orientation of the deep layer moisture transport to the terrain, should favor rainfall rates still reaching as high as 0.50" to 1"/hour for the favored upslope areas over the next several hours. The coastal ranges near and outside the Bay Area, along with the interior foothills of the Sierra Nevada west and northwest of Lake Tahoe will see the heaviest rates. An additional 2 to 4 inches of rain is expected for the higher terrain, with a few isolated heavier totals going through the midday time frame. Lower amounts are expected for the interior valleys, but these heavy rains may lead to areas of flooding, and there will be some concerns that the heavier rainfall rates may encourage localized flash flooding and debris flow activity around some of the regional burn scars. Orrison ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!7WBqpHfFVKpNj9deuvDF9aDfIzhUEOfQE3Lqou34RgEiDBc-EnIJHr5yTHakK-QKlOnY= -aoFUCqQ8_OifYNAVKEr1HQ$ for graphic product... ATTN...WFO...EKA...HNX...LOX...MFR...MTR...REV...STO...VEF... ATTN...RFC...CNRFC...NWRFC...NWC... LAT...LON 42792437 42772370 42322351 41772342 41682309=20 41422287 41272240 40992178 40042129 39412045=20 38922007 38331973 37171853 36851892 37141947=20 37242001 37172068 36792106 36342122 35512081=20 35312114 35942184 36672212 37162269 37632299=20 38562369 39442409 40412462 41442429 42302445=20 =20=20=20=20=20=20=20=20=20=20=20=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) .