Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 302 PM EDT Mon Mar 10 2025 Valid 00Z Tue Mar 11 2025 - 00Z Fri Mar 14 2025 ...The West... Days 2-3... ...Impactful heavy snow from the California mountain ranges Wednesday to the Intermoutnain West late week. Please see current Key Messages below... An upper-level trough in the northeast Pacific will direct an atmospheric river at California starting Tuesday night and continuing through Wednesday. Mountain snow begins Tuesday night from the Cascade Range on south to the Siskiyou/Shasta and northern Sierra Nevada. By 18Z Wednesday, ECMWF SATs shows a SWrly >400 kg/m/s IVT that surpasses the 97.5 climatological percentile over central California. This enhanced moisture transport combined with a cold frontal passage and falling heights aloft will result if plummeting snow levels Wednesday night along the Sierra Nevada with heavy snow as low as 5,000ft in elevation. Hourly snowfall rates between 2-3"/hr are expected in these ranges, with the combination of heavy/wet snow also posing a potential risk for scattered areas of power outages and tree damage. Snow will also unfold into the Southern California ranges north and east of Los Angeles and San Diego Wednesday night and into Thursday morning. Minor snow accumulations are possible as low as 4,000ft in the San Rafael, San Gabriel, and San Bernadino Mountains through the day on Thursday. WPC probabilities between 00Z Wed - 00Z Fri show high chances (>70%) for snowfall totals >24" along the entire length of the Sierra Nevada above 6,000ft. Some areas above 8,000ft could see as much as 4-5 feet of snowfall by the time a break in the snow arrives Thursday night. The WSSI is depicting Major to Extreme Impacts in the Sierra Nevada that is driven due to the Snow Amount algorithm, as well as some inclusion of the Snow Load and Blowing Snow elements as well. Note that the Cascades above 4,000ft and Olympics above 3,000ft have high chances (>70%) for snowfall accumulations >6" through Thursday afternoon. East of the Pacific Mountain ranges, the expansive swath of Pacific moisture will expand well inland Wednesday night and into the second half of the week. The heaviest snowfall is likely to occur on Thursday as the cold front sweeps across the Intermountain West and the diffluent left-exit region of a 250mb jet streak positions itself overhead. Snow is likely to continue a little longer into Tuesday night and Friday, so for more on those potential snowfall details, please refer to our medium range discussion. WPC probabilities through 00Z Friday depict high chances (>70%) for snowfall >8" in parts of the Blue, Sawtooth, central and southern Nevada terrain, portions of the Wasatch, and the tallest peaks of the Mogollon Rim. Mullinax https://www.wpc.ncep.noaa.gov/key_messages/LatestKeyMessage_1.png