Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 358 AM EDT Thu Mar 28 2024 Valid 12Z Thu Mar 28 2024 - 12Z Sun Mar 31 2024 ...The West... Days 1-3... With a closed upper low nearly stalled off the coast of British Columbia early this morning, a piece of energy shedding out of it will continue to move through the Pacific Northwest and Rockies today. A cold front, currently draped along the Cascades will continue to move eastward, allowing snow levels to drop considerably to around 3000 to 4000 ft in its wake. This will bring heavy snowfall to most of the mountain ranges including the Olympics, Cascades, the Shasta-Siskiyou, Sierra Nevada and eastward including Unitas and western WY ranges. In most of these locations, 8" snow probabilities are high and some of the higher peaks could top 12-18" over the next few days. A secondary reinforcing shortwave trough will approach the California coast Friday/Friday evening, closing off just offshore by 00Z Saturday. This will direct another plume of moisture and lift into the region and bring widespread moderate to locally heavy precipitation to parts of California. Snow levels are expected to be around 5000 ft in the Sierra and between 5000-5500 ft across the SoCal ranges. Day 2-3 snow probabilities are high for at least 12 inches across the Sierra and are at least moderate (40-50 percent) for the highest peaks of the Transverse and Peninsular ranges. By Day 3, some of that moisture spills eastward bringing another round of heavy snow to the southern UT mountains, the Unitas, and portions of the CO Rockies where 6" probabilities are above 50 percent. ...New England... Days 1-2... Phasing pieces of shortwave energy over the East Coast today through Friday will take an area of low pressure currently organizing along a stationary boundary across the Carolinas north/northeast toward coastal New England and the Gulf of Maine by Friday afternoon. As the low approaches coastal New England, precipitation is expected to spread inland with a frontogenetical band on the northwest/west side of the low. Guidance clustering has improved somewhat this cycle with respect to the low track but the thermal profiles on the western side (and possible snowfall accumulations) remains more uncertain. The NAM/NAM3km is the most aggressive with the depth of the cold air while the GFS and CMC is warmer and/or further to east, limiting the amount of snowfall accumulations. For now, a blend of the available guidance trends well with continuity and the latest WPC snow probabilities are moderate (40-60 percent) for at least 4 inches from the higher peaks of the White Mountains in NH and across northern Maine. ...Northern Plains... Day 2... An embedded shortwave trough moving onshore the Pacific Northwest this morning will quickly lift northeast through the Rockies today and into the Northern Plains by Friday. Broad isentropic lift overrunning a warm front in the region and upper level diffluence from the approaching shortwave will yield a quick shot of forcing for ascent and precipitation. Snowfall totals across northern North Dakota and northern Minnesota may approach a few inches and the latest snow probabilities for 4 inches are up to 30 percent. Taylor