Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 356 AM EST Sun Jan 01 2023 Valid 12Z Sun Jan 01 2023 - 12Z Wed Jan 04 2023 ...Western U.S.... Days 1-2... The ongoing atmospheric River impacting the Western U.S. will begin to move inland and approach the Four Corners region later today/tonight. The shortwave energy is forecast to close off over the Four Corners by early Monday morning and the combination of the enhanced lift, orographic effects, and higher moisture in place will bring widespread moderate to locally heavy snowfall to the terrain areas from northern AZ, much of UT, WY, and western CO. Probabilities are high for 8-12" for the highest terrain areas with some locations likely to see totals of 1-2 feet through the storm, particularly across the central Rockies, Mogollon Rim in Arizona, and San Juans in CO. A weaker storm system from the Pacific is forecast to reach the West Coast by Monday evening, with moderate snow reaching the northern California mountains and then the Sierra by overnight Monday and into Tuesday morning. This low will likely take a more southerly route compared to the ongoing event, with some additional snow for the higher terrain of Arizona and western New Mexico on Tuesday as the system continues to weaken. ...Central Plains and Upper Midwest... Days 2-3... As the shortwave energy swings across the Four Corners and Rockies tonight into Monday, an area of low pressure is forecast to develop over southeastern Colorado before racing northeastward toward the Upper Midwest through Tuesday night. The increasingly negatively tilted shortwave trough will promote a broad area of forcing that will help bring anomalously high moisture further north, wrapping into the system. The tight baroclinic zone expected to develop across portions of the Plains will lead to a strong frontogenetical band of moderate to heavy snow late Monday through early Tuesday where soundings show a favorable overlap of maximum lift with the DGZ to support enhanced snow rates above 1"/hr. Further to the south/southeast, a warm nose punching northward will likely bring a transition zone of mixed precipitation with a relatively deep surface cold layer supporting freezing rain and potentially significant ice accumulations in a narrow corridor from northeast Nebraska, southeast South Dakota, and northwest Iowa, tapering off some into southern Minnesota. Finally, by Tuesday into Wednesday, the shortwave energy opens up, becoming absorbed into the longwave troughing over the region. Some lingering deformation band snow will likely continue for portions of northern Wisconsin into the U.P. of Michigan. The latest WPC snow probabilities show high probabilities for at least 8 inches across northern NE and southern SD as well into southwest Minnesota while localized totals over 12 inches are likely across south-central SD. Across central Minnesota, northwest WI into the U.P. of Michigan, 8" probabilities reach moderate levels for day 2-3 (30-50 percent), greatest across central Minnesota around the MSP metro. Some significant ice accumulations will be possible from northeast NE through southwest into southern MN where 0.1" ice accretion is above 90 percent while 0.25"+ probabilities are up to 40-50 percent across northwest IA. A secondary area of freezing rain and ice accumulation exists for central/north-central WI where 0.1" probabilities are between 40-60 percent. Taylor ...Key Messages for January 1-3 Winter Storm... -An area of low pressure will develop and bring snowfall to the central High Plains beginning later tonight. This low pressure will intensify as it tracks northeast into the Great Lakes by Tuesday, producing a large swath of moderate to heavy snow, sleet, and freezing rain. -Snow rates exceeding 1â€/hr are likely in the heavy snow swath and combined with strong winds, areas of blowing snow will create snow-covered roads and difficult travel. -Localized significant ice accumulations exceeding 0.25†are possible from portions of northeastern Nebraska, northwest Iowa into southern Minnesota. This may lead to dangerous travel and isolated power outages. -There remains some uncertainty in the exact storm track and potential mixed precipitation types and zones. Stay updated to the latest forecast information.