Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Mar 12 2023 22:24:45 AWUS01 KWNH 122224 FFGMPD CAZ000-ORZ000-130915- Mesoscale Precipitation Discussion 0102 NWS Weather Prediction Center College Park MD 623 PM EDT Sun Mar 12 2023 Areas affected...northern CA into southwestern OR Concerning...Heavy rainfall Valid 122222Z - 130915Z Summary...Periods of moderate to heavy rain are expected to affect parts of northern CA into southwestern OR over the next 6-12 hours. While rainfall rates are expected to mostly remain below 0.5 in/hr, the potential for 12 hour totals of 1-2 inches, locally near 3 inches, will be falling on wet antecedent conditions due to precipitation over the past 14 days. Discussion...Water vapor imagery at 22Z showed a couple of vorticity maxima embedded in WSW flow off of the northern coast of CA. Another was inland over central OR. The mid-level vorticity center nearest to the northern CA coast was associated with an approaching region of higher reflectivity values on local radar, with rain just starting to move inland. 850-700 mb winds were S to SW at KBHX near 35 kt and precipitable water values were 0.6 to 0.9 inches along the southern OR to northern CA coast. Water vapor imagery also showed an upper level trough to the west of Vancouver Island with upper flow more backed to its east relative to upper level winds to the west of northern CA. A cold front containing a couple of weak waves were analyzed ahead of the upper trough over the eastern Pacific at 22Z. Any instability in place along the coast is thought to be too low to be of any significance. The eastward to northeastward translation of the upper trough to the north and vorticity maxima to the south will support an increase in areas of moderate to heavy rain moving inland across northern CA and southern OR over the next several hours. Flow aloft is also forecast to become more diffluent tonight ahead of the approaching upper trough off of Vancouver Island. Onshore flow is forecast by the RAP to increase slightly into the 35-45 kt range, favoring south to southwest facing slopes of the Coastal Ranges for upslope enhancement. However, only marginally anomalous precipitable water values and a lack of significant instability should keep rainfall rates below 0.5 in/hr. Snow levels are forecast to remain fairly steady, ranging between 5500 and 6500 ft into the overnight. While these rainfall totals/rates below freezing levels should not be problematic in terms of flooding, the region has picked up 150 to 300 percent of normal precipitation over the past 2 weeks, leaving soil moisture values fairly high compared to historical averages. Given the wet antecedent conditions, very localized flooding may occur due to the addition of 1-3 inches of rainfall through 09Z. Otto ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!5GF-AFWonwUYalODT2EefrMThfwPl20g7HdnTXnMO-6_-pg7reGTgiA8_QbhhlESImex= MfroTmiMMYE2iMPQQFWCBVg$ for graphic product... ATTN...WFO...EKA...MFR...STO... ATTN...RFC...CNRFC...NWRFC...NWC... LAT...LON 42872434 42792408 42812388 42642367 42292366=20 42112363 42042360 42042347 42052331 42012323=20 41972317 41842316 41742318 41682318 41612316=20 41452313 41292306 41172305 41032307 40982309=20 40932306 40902297 40912284 41112269 41162252=20 41322224 41382209 41392193 41332176 41112162=20 40862180 40652209 40572249 40322276 40052276=20 39802280 39552338 39532394 39872430 40342474=20 41362456 42352474 42792464=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) .