Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 432 PM EDT Mon Apr 20 2020 Valid 00Z Tue Apr 21 2020 - 00Z Fri Apr 24 2020 ...Northeast... Days 1-2 (00Z Tue - 00Z Thu)... An upper low will continue to develop north of the Great Lakes Monday night. Models show the system beginning to assume a negative tilt with a strong surface cold front sweeping across much of the Northeast on Tuesday. By late Tuesday, a secondary low developing near coastal Maine is forecast to lift north into Atlantic Canada overnight. Overall, expect generally light snow accumulations east of the Great Lakes and across Upstate New York and central to northern New England, with locally heavier totals possible across portions of the higher terrain. For the two day period, WPC PWPF shows probabilities of 50 percent or greater for snow accumulations of 4-inches or more across portions of the Adirondacks, White Mountains and across much of northern Maine. ...Central and Southern Rockies... Day 1 (00Z Tue - 00Z Wed)... A progressive southern stream shortwave is expected to support periods of snow across the mountains of Utah, Colorado and far northern New Mexico. While widespread heavy accumulations are not expected, WPC PWPF does show some low probabilities for accumulations of 8-inches or more across portions of the southern Utah mountains as well as the San Juan Mountains. ...Northern and Central Rockies... Day 3 (00Z Thu - 00Z Fri)... Mid-to-upper level energy embedded within developing northwest flow, along with areas of favorable upper jet forcing, will support periods of snow across the region. Areas impacted are expected to include the northern and central Idaho and the western Montana to the western and central Wyoming ranges. While widespread heavy amounts are not expected, WPC PWPF does show the potential for localized accumulations of 6-inches or more across those areas. For Days 1-3, the probability of significant icing (0.25-inch or greater) is less than 10 percent. Pereira