Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Mar 13 2023 18:51:41 AWUS01 KWNH 131851 FFGMPD CAZ000-ORZ000-140500- Mesoscale Precipitation Discussion 0104 NWS Weather Prediction Center College Park MD 251 PM EDT Mon Mar 13 2023 Areas affected...southwestern OR into northern CA Concerning...Heavy rainfall...Flash flooding possible Valid 131850Z - 140500Z Summary...Moderate to heavy rain will continue to impact portions of southwestern OR into northern CA through the day, with the threat tapering off early tonight. Additional rainfall totals of 1 to 3 inches, with locally higher values possible, are expected through 05Z with occasional peak rainfall rates in the 0.5 to 0.8 in/hr range. Discussion...Regional radar imagery over the past few hours through 18Z and surface observations showed moderate to heavy rain affecting locations from far northern Mendocino County, CA into Curry and Josephine counties of southwestern OR. Snow levels were estimated to be 5500-6000 ft at 18Z for the entire region. Water vapor imagery from GOES West showed a pronounced mid to upper-level trough axis advancing eastward toward the Pacific Northwest. The heaviest rain was occurring just ahead of the attendant cold front where southwesterly flow of 40-50 kt in the 850-700 mb layer was occurring with precipitable water values of 0.6 to 0.9 inches along the coast. Flow in the upper levels was diffluent just west of the OR/CA border, out ahead of a 100-110 kt jet streak tracking through the base of the upper trough. As the upper trough axis continues to translate eastward into the evening, the cold front along the coast will slowly settle southeastward and increasingly favorable upper level forcing will reach the coast late this afternoon/early evening. The axis of greatest low level moisture transport will follow suit into northern CA with snow levels falling sharply behind the cold front across southwestern OR. Periods of moderate to heavy rain, with occasional rates in the 0.5 to 0.8 in/hr range will be possible along southwest facing slopes of the Coastal Ranges into the lower elevations of the Klamath, Trinity, Shasta and Cascade Ranges/Mountains. Additional rainfall through 05Z is expected to range from 1 to 3 inches, but very localized higher totals will be possible. Given these rains falling on existing areas of snow cover, along with saturated soils and swollen rivers/creeks/streams, the combination of snowmelt and runoff will contribute to the potential for flooding. Beyond 03Z, precipitation intensity will begin to wane for far northern CA as low level moisture transport weakens and the focus shifts to the south, in advance of an approaching atmospheric river advancing toward central CA. Otto ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!8M4aBLZqHcXl98HdEwly6sUPzUdDT84-1Fv1PGg28h7JnxLP4L7qClPnMZ4ipUZ-XmtX= jdsWUJ4wleMBkwKNVvG1Pyw$ for graphic product... ATTN...WFO...EKA...MFR...STO... ATTN...RFC...CNRFC...NWRFC...NWC... LAT...LON 42702447 42692384 42532349 42362318 42272306=20 41932277 41652279 41422254 41432211 41432203=20 41492187 41552168 41512151 41312152 40972184=20 40742221 40472265 40262307 39822320 39522390=20 39852440 40132457 40902484 41512481 42042491=20 42372487=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) .