Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 459 PM EST Wed Nov 22 2023 Valid 00Z Thu Nov 23 2023 - 00Z Sun Nov 26 2023 ...Northeast... Days 1-2... Ongoing precipitation across Maine will be ending this evening as the associated low moves east into Atlantic Canada. Upstream energy embedded within deep cyclonic flow is expected to bring snow showers back into portions of northern New York and New England Thursday night and Friday. Overall, accumulations are expected to be light. ...Northern Rockies to the Central Rockies and High Plains... Days 1-3... Overall, models have remained consistent with the winter storm that is expected to develop initially over the northern Rockies on Thanksgiving, before shifting farther south into the central Rockies on High Plains on Friday. While the details remain more uncertain, there has been a growing signal for impactful snow moving east from western to central Kansas on Saturday. Snow is expected to initially develop on Thanksgiving across the northern Rockies and extend into portions of the High Plains as an amplifying mid-to-upper level shortwave dives south from western Canada, with a closed low developing over the interior Northwest and northern Great Basin by late in the day. Meanwhile, a strong cold front will be dropping south, bringing much colder air into the region. Increasing upslope flow on the west side of a 1040 mb high sinking into the northern Plains, in combination with low-to-mid level frontogenesis and favorable upper jet forcing will contribute to the expansion of snow across portions of southern Montana and northern Wyoming, with the heaviest snows expected to develop along the favored terrain. As the upper low continues to deepen and drop southeast, heavy snow is likely across portions of Wyoming Thursday night into Friday, with several inches likely in the mountains. Lighter, but impactful amounts are expected east of the terrain along a low-to-mid level front extending out into the Nebraska Panhandle. Snow is forecast to spread south into central Rockies, impacting portions of northern Utah and northern Colorado by early Friday. By late Friday and continuing into early Saturday, deep southwesterly flow ahead of the low along with shortwave energy moving south of the center will support the development of heavy snow farther south across the San Juan Mountains. Models show the upper low transitioning to an open wave with this energy moving east into the central High Plains on Saturday. While the details are far from certain, models suggest that increasing ascent afforded by the approaching wave and low level frontogenesis may contribute to an area of moderate to heavy snow developing across portions of western to central Kansas. WPC probabilities indicate that storm total amounts are likely (greater than 70 percent) across the Wyoming ranges from the Absaroka, Wind River, and Big Horns to the Laramie and Medicine Bow mountains. Similar probabilities are shown across the central to southern Colorado ranges. Locally heavier totals of a foot or more can be expected in these areas. Moderate probabilities (40 to 70 percent) for accumulations of 6 inches or more extend from the Nebraska Panhandle south into far northeastern Colorado and northwestern Kansas. Pereira ***Key Messages for Thanksgiving Snowstorm*** --Much colder temperatures for the Rockies A strong cold front over Canada will push southward today, bringing much colder air to the northern Rockies. Light snow will gradually expand in coverage over Montana as the cold air sinks southward. --Heaviest snow most likely over Wyoming and Colorado Snow will increase on Thanksgiving over Wyoming and progress southward into Colorado overnight into Friday. There is a high (>70%) chance of at least 6 inches of snowfall through Saturday over parts of Wyoming and Colorado. Lighter amounts are forecast elsewhere in the Rockies and over the High Plains. --Impactful snow possible across portions of the central Plains There is increasing confidence that light to moderate snow will develop and move east across western to central Kansas Friday night and Saturday. --Impacts to travel from snow, wind, and icy roads Snowfall rates of 1" per hour will make travel difficult on busy interstates such as I-25, I-80, and I-90. Blowing snow will locally reduce visibility. The arctic front may cause flash freezes in Utah, Southern Wyoming, Colorado, and the Nebraska Panhandle Thursday (Thanksgiving) evening as temperatures rapidly drop below freezing.