Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 517 AM EDT Sun Apr 11 2021 Valid 12Z Sun Apr 11 2021 - 12Z Wed Apr 14 2021 ....Northern Plains... Days 1-3... An amplifying shortwave trough and its associated frontal band will continue to move east of the northern Rockies into the Plains this morning. Models continue to show an area of enhanced precipitation centered along an elongated low-to-mid level center sliding across North Dakota on Sunday. Thermal profiles suggest a rain/snow mix during the day on Sunday, changing to mostly 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 (ending 12Z Monday) shows a small area of 30-50 percent probabilities for accumulations of 4-inches or more. Models show an elongating upper low developing over the northern Plains by early Monday, with snow spreading across northern Minnesota and North Dakota. Periods of snow are expected to continue through Tuesday and into early Wednesday as the low drifts slowly east, resulting in widespread but generally light 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 the the northwestern corner of Minnesota. ...Great Basin to the Central Rockies... Day 3... A shortwave trough dropping south from western Canada on Monday, is expected to develop a closed low over the Pacific Northwest and northern Intermountain West on Tuesday. Divergence aloft will support snow developing across northern Nevada and southern Idaho, northern Utah, and western Wyoming by late Tuesday and then continuing into early Wednesday. In addition to favorable upper dynamics, increasing upslope flow will begin to support snow developing along the High Plains into the eastern slopes of the central Rockies, with some potential for significant accumulations beginning to develop along the southeastern Wyoming and central Colorado ranges by early Wednesday. For Days 1-3, the probability of significant icing (0.25-inch or greater) is less than 10 percent. Pereira