Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 416 PM EDT Sat Mar 21 2020 Valid 00Z Sun Mar 22 2020 - 00Z Wed Mar 25 2020 ...Northeast... Days 2-3... Low pressure developing near the VA/NC coast early Monday will lift northeast off the New England coast through Tuesday. This low will develop and deepen in response to a shortwave moving out of the Upper Midwest and increasing diffluence on the LFQ of a subtropical jet streak pivoting northeast. As the low lifts towards the benchmark, strong WAA will spread northward through the Mid-Atlantic and northeast. Initially, the column will be cold enough for all snow from the Laurel Highlands of PA, northeast into all of New England. The strong WAA will likely produce a burst of snow across these areas, but persistent warming of the column will gradually change the p-type from snow to rain as far north as southern New England. Although snow is likely to remain the primary p-type across upstate New York and central New England/northern New England, precipitation across those areas is likely to be less robust than points further south. This suggests the heaviest snowfall is likely in the elevated terrain of New York and southern/central New England, where WPC probabilities are high for 4 inches. The heaviest snow amounts, possibly exceeding 6 inches, are expected in the Catskills, Berkshires, Southern Greens, Wapacks, Northern Worcester Hills, and potentially into the White Mountains as well. Elsewhere, a slushy 1-3" is likely, with a quick light accumulation even possible in NYC and Boston. ...Mountains of California, the Great Basin, and Four Corners... Days 1-3... Lingering moisture and snowfall beneath the finally decaying and shearing upper low will wind down on D1 across the San Juans and Rockies of Colorado. WPC probabilities for 4 inches are moderate, and confined to areas above 6000 ft. Late on Sunday, a renewed upper low will drift towards the CA coast. South of the low is expected to be a 130kt subtropical jet that streams across southern CA. This jet produces strong ascent and moisture fluxes into California. As 700mb flow becomes increasingly orthogonal to the Sierra, heavy snow will develop and spread northeastward. WPC probabilities on D2/Sunday are high for 8 inches, with localized amounts over 12 inches likely. As the 700 mb wave progresses inland into the southwest, both the moisture plume and ascent cross NV into UT and western CO, so light snows should pick up Mon in the UT Wasatch and then mountains of western CO. Given modest ascent and a deamplifying mid level wave, potential for heavy snow is limited, and WPC probabilities for 6 inches are low and limited to the highest peaks of the Wasatch, Uintas, and Colorado Rockies. ...Mountains of the Pacific Northwest to the Northern Rockies... Day 3... Potent closed mid-level low will drop southward along the coast of British Columbia towards Washington State, accompanied by a weak surface low and modest upper level diffluence. Moist advection will stream eastward well inland from Washington through Montana and Wyoming south of the mid-level feature. Increasing 700-500mb RH and ascent along a mid-level front will drive increasing precipitation across this area, with snowfall developing and accumulating during Tuesday. Snow levels will fall from around 3000 ft early, to as low as 1000 ft, and WPC probabilities for 6 inches are moderate for the Olympics, Cascades of WA and OR, and eastward into the Sawtooth and Northern Rockies. The probability of greater than 0.25 inches of freezing rain is less than 10 percent. Weiss