Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Dec 27 2024 02:46:32 AWUS01 KWNH 270246 FFGMPD CAZ000-ORZ000-271200- Mesoscale Precipitation Discussion 1195 NWS Weather Prediction Center College Park MD 945 PM EST Thu Dec 26 2024 Areas affected...Southwest OR...Northern and Central CA Concerning...Heavy rainfall Valid 270245Z - 271200Z SUMMARY...New atmospheric river surge arriving overnight will bring additional rounds of heavy rainfall and potentially some localized flooding and runoff concerns. DISCUSSION...The latest GOES-W Airmass RGB satellite imagery shows a new shortwave trough amplifying offshore of the West Coast which will drive a new area of cyclogenesis overnight. The developing low center will arrive across the coastal ranges of northwest OR and southwest WA by early Friday morning. To the south of this low center will be a renewed deep layer fetch of Pacific moisture that will overrun the coastal ranges down the coast, and especially across southwest OR and into northern and central CA. A warm front offshore of the West Coast will be approaching as rather strong IVT magnitudes encroach on the region. Enhanced low to mid-level flow around the southern flank of the shortwave trough will drive IVT values upwards of 750 to 1000 kg/m/s at least for several hours (generally between 03Z and 09Z) as the warm front arrives and advances inland. Later tonight and toward 12Z, the low center entering the Pacific Northwest will drive a cold front inland across the coastal ranges. PWs are forecast to reach as high as 1 to 1.25+ inches, and reaching locally as high as 2 to 3+ standard deviations above normal with the greater anomalies forecast to set up in the 06Z to 12Z time frame down across the Bay Area. Even areas a bit farther south down the coast around Monterey are expected to see a notable increase in PWs overnight as this latest atmospheric river surge arrives. The latest HREF guidance shows rather high probabilities of seeing at least a few hours of potential 0.50"+/hour rainfall rates impacting the orographically favored terrain from southwest OR down through northwest CA and also portions of the Bay Area in the 06Z to 12Z time frame. Some of these heavier rains may also at least locally spillover into the far northern Sacramento Valley and the foothills of the northern Sierra Nevada, but generally the heaviest rates should be across the coastal ranges. This will coincide with the strongest window of forcing from warm air advection and higher IVT parameters. After 12Z, the rates should diminish rather substantially as the energy associated this latest system advances rapidly inland. Additional rainfall totals going through 12Z (4AM PST) Friday morning are expected to reach 2 to 3 inches with isolated heavier amounts possible. Given the wet antecedent conditions, these additional rains may result in some localized flooding concerns and this will include some urban flooding potential around the Bay Area tonight. Orrison ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!8784PPpwQjwvhq15F2dET7JKppLElsnfqNyj9XokRKUxZ74gHfsylSnY2rK2uCnw_wQK= 8WHCS1WHNlAuclfAjx9eiDQ$ for graphic product... ATTN...WFO...EKA...MFR...MTR...REV...STO... ATTN...RFC...CNRFC...NWRFC...NWC... LAT...LON 43142392 42382323 41932229 41422172 41052171=20 40552133 40062088 39642075 39182077 39102137=20 40002199 39922247 39572247 38952222 38262196=20 37342135 36822148 36582193 36972258 38182341=20 39262412 40792456 41792449 42912460=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) .