Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 414 AM EDT Sat Mar 27 2021 Valid 12Z Sat Mar 27 2021 - 12Z Tue Mar 30 2021 ...Pacific Northwest to the Northern Rockies... Days 2-3... Heavy snow is expected to return to the mountains of the Pacific Northwest with the approach of an intensifying 700 mb wave, bringing a surge in integrated water vapor transport and ascent across the WA Cascades Sunday. Accumulations around a foot are likely by Sunday evening across the higher elevations of the Olympics and locally as much as 18-24 inches in favored windward locations in the northern Cascades. Drying aloft eases snowfall coverage and intensity Monday in the Cascades. The surge in moisture advection and lift that crosses the Pacific Northwest Sunday moves inland across the northern Rockies Sunday night and early Monday. Although the 700 mb wave moves quickly east across the northern Plains Monday, residual moisture remains in place in the ranges of western MT Monday, with confluent flow and upper level jet max supporting additional periods of ascent, with several additional inches of snow expected. The low-mid level flow advects moisture downstream into the Beartooth and Teton Ranges Sunday, where several inches of snow are expected in favored upslope areas. Widespread accumulations of 8 inches or more are likely across the mountains of northwestern Montana. Locally heavier amounts on the order of 12-18 inches are most likely in the northwestern Montana ranges for Sunday and Monday combined. WPC shows high probabilities for accumulations exceeding a foot over the northern Cascades and ranges of northwest MT. ...Northeast... Day 2... The models show a deep layer of warm/moisture advection moving across northern New England Sunday. This occurs underneath a jet streak aloft, with the combination leading to steady precipitation, including an extended period of snow across northern Maine. The warm advection results in a change over to rain in most of southern Maine. PWPF shows high probabilities for 4 inches or greater across a good portion of northern Maine. It also indicates 30 percent or greater probabilities for amounts of 8-inches or more across northern Aroostook County. The event winds down as the upper trough passes early Sunday with drying aloft sharply reducing snow coverage/intensity. The limited duration of the event keeps probabilities for heavy snow limited. ...Northern Minnesota... Day 1... A 700 mb shortwave moving east across MN today will lead to a period of enhanced moisture and lift within a couple upper jet pattern. The 850-500 mb ascent leads to a period of snow across northeast MN, with The trough progresses east overnight As the 700 mb trough passes, drying aloft brings the the Southwest, is forecast to lift northeast from the central Plains into the Upper Midwest ahead of a northern stream trough moving through the Dakotas on Saturday. Models show precipitation developing as or changing to snow along and behind the northern stream boundary as it drifts across northern Minnesota on Saturday. This will likely produce two to four inches of snow across the Arrowhead, with a low probability of 4 inches. For Days 1-3, the probability of significant icing (0.25 inch or more) is less than 10 percent. Petersen