Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Dec 28 2024 03:07:44 AWUS01 KWNH 280307 FFGMPD CAZ000-ORZ000-281300- Mesoscale Precipitation Discussion 1198 NWS Weather Prediction Center College Park MD 1007 PM EST Fri Dec 27 2024 Areas affected...Southwest OR...Northwest CA Concerning...Heavy rainfall Valid 280305Z - 281300Z SUMMARY...The latest in a series of atmospheric river surges will be arriving overnight across southwest OR and northwest CA with a new round of focused heavy rain over the coastal ranges. DISCUSSION...The GOES-W Airmass RGB satellite imagery shows another strong shortwave trough gradually approaching the Pacific Northwest which will be favoring the arrival of a new area of deepening surface low pressure near Vancouver Island by early Saturday morning. To the south of this low center evolution, a renewed deep layer surge of Pacific moisture and associated atmospheric river activity will be overrunning the coastal ranges of southwest OR and northwest CA. Strong low to mid-level westerly Pacific flow overnight will allow a warm front to approach the region and advance quickly inland across northern CA, with a trailing cold front that will then gradually begin to cross the coastal ranges by early Saturday morning. IVT magnitudes will rise rather sharply over the next several hours across especially southwest OR and far northwest CA, including Coos, Curry and Del Norte Counties, with values increasing to over 750 kg/m/s by 06Z. Enhanced warm air advection and moisture transport into the orographically favored terrain will likely result in rainfall rates approaching and locally exceeding a 0.50"/hour. The 18Z HREF guidance shows elevated probabilities (50 to 70 percent) of this occurring with potentially some brief 0.75"/hour rates occurring as the IVT values peak overnight just ahead of the approaching offshore cold front. The IVT magnitudes will then be dropping off in the 09Z to 12Z time frame which will allow for the rainfall rates and shower activity to at least diminish early Saturday morning, but the aforementioned cold front that arrives will also be tending to slow down which will keep the front in close proximity to the coastal ranges of northwest CA through Saturday morning. Additional rainfall amounts going through 12Z of 2 to 4 inches are likely for especially the coastal ranges of southwest OR and northwest CA, with isolated heavier amounts. Given the already wet antecedent conditions and high streamflows, these rains are expected to foster at least some localized concerns for runoff problems and flooding. Orrison ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!5S2qpY0yCgrlh_Xu6QoJd_NKFF2_brL_2Dv6RidVoWup7OYz2RXzF2_zPVJ7mN5N1bJ2= MNpWRLOtTJjCB_69u5oY1Dw$ for graphic product... ATTN...WFO...EKA...MFR...PQR...STO... ATTN...RFC...CNRFC...NWRFC...NWC... LAT...LON 43822300 43242210 42362196 41802203 41332170=20 40812165 40012113 39812140 40222251 39862285=20 39442332 39442397 40012446 40372455 41322425=20 42042466 42782479 43542448=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) .