Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 341 PM EST Mon Mar 3 2025 Valid 00Z Tue Mar 04 2025 - 00Z Fri Mar 07 2025 ...Central Rockies and High Plains to the Upper Midwest... Days 1-3... ...A powerful storm will move into the central U.S. tonight Tuesday, producing multiple hazards through Wednesday, including periods of heavy snow from the central High Plains to the northern Great Lakes, as well as blizzard conditions across parts of the central Plains and strong winds throughout the Plains... A deep upper low is forecast to continue its track across the western U.S., rolling out from the central Rockies into the High Plains tonight. Snow will continue to spread across the central Rockies, with several more inches likely across the western to central Colorado ranges before diminishing on Tuesday. Meanwhile, rain changing to wind-driven snow is expected to develop on the backside of the surface cyclone deepening over eastern Colorado this evening. Increasing low level moisture advection into an area of strong ascent afforded in part by low- to-mid level frontogenesis, upper jet forcing, and orographic ascent will support the development of heavy snow along the northwestern to western extent of the low -- impacting areas from the Colorado Palmer Divide northeastward through portions of western Nebraska and into parts of western and central South Dakota tonight into Tuesday. While marginal temperatures may keep accumulations in check at the onset, heavy rates (1-2+ in/hr) after the changeover to snow is expected to produce areas of locally heavier amounts, with WPC guidance showing higher probabilities ( greater than 50 percent) for accumulations of 4 inches or more across portions of the region. Low-to-mid level frontogenesis will help extend a stripe of rain changing to snow further to the northeast through eastern South Dakota into central Minnesota, but guidance indicates snowfall accumulations across those areas will remain light through 00Z Wednesday. By late Tuesday, guidance shows a deep, nearly vertically-stacked low moving moving into the lower Missouri and mid Mississippi valleys. Models show a powerful low level jet drawing moisture into an area of strong ascent generated by a coupled upper jet and low- to-mid level forcing. Dynamic cooling will support rain changing to snow, with some guidance indicating heavy snowfall rates of 1-2 in/hr quickly developing within the associated comma head as it extends from portions of eastern Kansas and western Missouri to southern Minnesota and Wisconsin late Tuesday into Wednesday. The models have trended wetter and colder in some areas, especially across parts of the lower Missouri valley, resulting in an uptick in probabilities for heavier accumulations. Influenced by an amplifying northern stream trough to its northwest, the storm is forecast to turn to the northeast, with heavy snow continuing to develop on its northwest side as it moves from the mid Mississippi Valley Tuesday night to the northern Great Lakes by late Wednesday. Strong forcing and moisture advection pivoting across southeastern Minnesota into central Wisconsin is expected to contribute to some of the higher storm totals, with WPC guidance showing high probabilities for accumulations greater than 6 inches across the region. Otherwise, WPC guidance indicates the heaviest amounts are most likely to fall across parts of northern Wisconsin and Upper Michigan, where the initial swath of synoptically driven snow, followed by lake effect showers will likely contribute to totals exceeding a foot in some locations. Even for areas where heavy snow does not occur, powerful winds will become a concern throughout much of the Plains into the Midwest, gusting to over 70 mph in some locations. Snow combined with wind will result in reduced visibility, with blizzard conditions likely to develop in some areas, especially across portions of the central Plains into the lower Missouri Valley on Tuesday. ...California, Great Basin, Southwest, and central Rockies... Days 2-3... A mid-to-upper level shortwave pivoting east ahead of a low dropping south from the Gulf of Alaska is expected to tap deeper Pacific moisture as it approaches the West Coast, drawing it across central into southern California beginning Wednesday afternoon, before directing it further south and east into the Southwest and Great Basin. Heavy snow will initially focus across the central to southern Sierra Nevada (above 9000 ft), where favorable upper dynamics in addition to orographics will contribute to higher rates. Then by late Wednesday and continuing into Thursday, the threat for heavy mountain snow will spread across the Great Basin, northern Arizona, and into the central Rockies. In addition to the Sierra Nevada, the greatest threat for snow amounts of 6 inches or more will include the Nevada, Utah, and west-central Wyoming ranges. Pereira ...Winter Storm Key Messages are in effect. Please see current Key Messages below... https://www.wpc.ncep.noaa.gov/key_messages/LatestKeyMessage_1.png