Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 450 PM EDT Sun Apr 11 2021 Valid 00Z Mon Apr 12 2021 - 00Z Thu Apr 15 2021 ....Northern Plains... Days 1-3... A deep layer trough and its associated frontal band will continue to drift east across the northern Plains tonight. Post-frontal cold advection in northern North Dakota leads to a precip type change over from rain to snow Sunday night. This is expected to produce a stripe of mostly light accumulations from northwestern to central North Dakota. Heaviest accumulations through early Monday are expected to center over northwestern North Dakota, where the Day 1 WPC PWPF shows an area of 60-80 percent probabilities for accumulations of 4 inches or more. With the initial ground and air temperatures above freezing, more accumulations is expected over grassy surface than roads. As the upper low/trough elongate and move east from North Dakota to Minnesota Monday night-early Tuesday, mid level deformation and frontogenesis persists over northeast North Dakota and northwest Minnesota. Periods of snow are expected to continue through Tuesday as the low drifts slowly east, resulting in widespread accumulations across the region. For the two-day period ending 12Z Wednesday, WPC PWPF shows high probabilities for accumulations of 4 inches or greater extending across much of northern North Dakota into northwestern Minnesota. ...Great Basin to the Central Rockies... Day 2/3... On Day 2, the models show confluent flow aloft leading to a jet streak over the CO Rockies to central high Plains. Low level convergence and modest upslope flow leads to light snow developing int he foothills and front range of the CO Rockies Tue. Several inches of snow are possible. The snow expands in coverage Tue night into Wed as a closed 700 mb low is forecast to develop over Nevada and move across northern Utah to near the Wyoming border by 0z Thu. Coupled divergence aloft/low level convergence will support snow developing across northern Nevada and southern Idaho, northern Utah, and western Wyoming Wednesday. Several inches of snow are expected in favored upslope areas of elevated terrain. Continuing upslope flow will begin to support more snow into the eastern slopes of the central Rockies, with some potential for significant accumulations along the southeastern Wyoming and central Colorado ranges. For Days 1-3, the probability of significant icing (0.25 inch or greater) is less than 10 percent. Petersen