Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 329 PM EDT Thu Mar 21 2019 Valid 00Z Fri Mar 22 2019 - 00Z Mon Mar 25 2019 ...CA/Great basin/Rockies... ...Days 1-3... The first system is an upper low that crosses from NV this evening and across UT overnight into CO Friday. Light to moderate snow are expected along the track of the low and accompanying mid level deformation zone from east central NV across the UT Wasatch and then ranges of west CO. southern Rockies. The heaviest snow Day 1 is expected in the San Juans of CO as both longer duration snows occur plus the favored 300 mb jet crosses this evening to aid in producing higher snow rates. WPC probabilities show a moderate risk for 12 inches in the San Juans On day 2, the event in UT and CO winds down as the upper trough continues moving east, with temps too warm on the CO plains to support snow as you head towards the KS border. Modest snows are expected in the cyclonic shear zone and upper divergence maxima cross the ranges of southern ID to adjacent northwest WY. Snow picks up again the Sierra Nevada range in CA as the next in the series of upper trough moves onshore, with upper divergence maxima and low-mid level warm/moisture advection in the region centered in the hours around 12z Sat. As this trough moves further inland later Sat, the snow relocates into the ranges of southern ID and northern UT, where favorable difluent flow aloft supports lift from associated 300 mb divergence maxima. Although widespread heavy accumulations are not expected, WPC probabilities indicate a slight risk for 8 inches in the Sawtooth range and eastward into NW WY. Several inches are expected in the UT Uintas due to the orographic lift plus synoptic lift from the approaching upper trough. ...Interior New York/Northern New England... Days 1-2... A surface low near the Delmarva today will move northeast across eastern New England into Maine on Friday and the Canadian maritimes thereafter, with slow forward motion. Snow occurred in the higher elevations of the VA Blue Ridge today and the forecasts continue to show an elevation based event as it crosses PA into New York tonight. The heaviest snow is expected in the band of enhanced mid level deformation and frontogenesis from higher elevations few the southern tier to the western Catskills of NY and the Adirondacks. Once the upper low passes later Friday, cold air returns from west to east, with post frontal upslope flow allowing snow in the Adirondacks to continue and then develop in the Green Mountains of VT and the Berkshires of MA. A relative minima in snow is expected in the Hudson Valley first due to initial warm temps and then descent in the lee of the Adirondacks. A mixture of precip types and duration provides the uncertainty in the Catskills of NY. The highest probabilities for 4 inches of snow are across the Adirondacks, due to the longer duration of snow . There is likely to be significant snowfall gradient in the terrain however, especially in the Champlain Valley of VT, which is between heavier snow corridors in the Adirondacks and Green Mountains. WPC probabilities show a moderate to high risk for 8 inches of accumulation in the highest terrain. Up in ME, the initial shot of warm advection zone then leads to a precip type transition plus a dry slot might cross the region. Precip transitions back to snow late Fri-Fri night as the 850 mb low moves across downeast Maine, providing a favorable track for western ME to get several inches of snow in the mid level deformation band. As the low pulls away slowly, NW flow will be favorable for upslope snow focuses snow in the mountains of WV, where several inches are possible, with more weighting given to the NAM and less weight to the 12z GFS, which has been changing its low level enough to warrant low confidence. The probability of significant freezing rain is less than 10 percent. Petersen