Subj : HVYSNOW: Probabilistic Heavy Snow And Icing Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Feb 24 2025 19:38:33 FOUS11 KWBC 241937 QPFHSD Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 237 PM EST Mon Feb 24 2025 Valid 00Z Tue Feb 25 2025 - 00Z Fri Feb 28 2025 ....Pacific Northwest through the Northern Rockies... Days 1-2... Our current AR over the Pacific Northwest is ongoing with the sat/radar composite outline a textbook warm frontal band of precipitation across coastal OR/WA. The cold front accompanying the surface low off the coast is already being analyzed off the northwestern CA and southwest OR coasts with light precip already situated along and ahead of the axis of frontal convergence. Deep moisture anomalies continue to be the driver of heavier precipitation potential with IVT's hovering between 400-600 kg/m/s during the strongest precip period occurring now through at least early Tuesday morning. IVT anomaly is squarely within 3-5 deviations above normal according to the latest NAEFS output, a typical marker for marginal AR intensity. This should provide sufficient deep layer moisture for heavier snowfall potential over the higher elevations of the Olympics and Cascades this afternoon, even as warmer air filters inland and snow levels rise into the evening. The guidance is still well aligned overall with the synoptic and mesoscale features, leading to high confidence in the evolution of this ongoing event. Consensus overnight did trend colder today in areas north of a draped front from west-east near the WA/OR border, but the propagation of the warm front will lead to snow levels rising incrementally through the afternoon and early evening hours across WA/ID/OR/MT. Thereafter, snow levels will plateau during the overnight time frame, then crash again quickly during front half of D2 as the aforementioned cold front off the Pacific coast pivots east accompanying falling heights aloft. Despite the lowering snow levels D2, this will occur in tandem with a drying column, which indicates most of the heavy snow should accumulate only at the higher elevations thanks to rapid wane of precipitation coverage and intensity by the second half of D2. WPC probabilities for heavy snow accumulating to more than 6 inches remain high (>90%) in the Olympics and along the crest of the Cascades the remainder of D1, with locally 2-3 feet possible at the highest elevations (Above 7000ft MSL). Additionally, impactful pass- level snow is likely especially at some of the higher passes like Washington Pass. During D2, heavy snow continues across the Cascades but also expands eastward towards the Northern Rockies. WPC probabilities D2 are high (>70%) for 6+ inches across the higher elevations of these ranges, before precipitation winds down into D3. Weiss/Kleebauer $$ = = = 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) .