Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 237 AM EST Fri Mar 10 2023 Valid 12Z Fri Mar 10 2023 - 12Z Mon Mar 13 2023 ...The West... Days 1-3... An ongoing atmospheric river event will continue through today, with additional very heavy precipitation forecast for central to southern California. Snow levels will remain above 8000 ft, confining the threat for heavy snow to the higher elevations of the central and southern Sierra, where several additional feet of heavy, wet snow is expected. Refer to the Key Messages below for additional information regarding the expected impacts across this region. Farther to the north, a deep, compact low will move across the Pacific Northwest today. This dynamic system is expected to produce moderate to heavy snow along its well-defined front as it sweeps across the Northwest and into the northern Rockies later today. Periods of heavy snow and strong gusty winds are expected as the front moves across the region. The snow squall parameter continues to indicate that snow squalls are likely to develop today across the interior Northwest into the northern Rockies. The low is expected to move east of the northern Rockies and into the High Plains as its trailing cold front drops south into the Great Basin and central Rockies, bringing the threat for heavy snow into parts of that region as well. While relatively quieter weather is expected across the Northwest and northern Rockies on Saturday, wet weather will continue across California, with additional heavy precipitation expected. Additional heavy snow accumulations are likely for the Sierra as snow levels decline, dropping below 6000 ft across much of the region by early Sunday. Backing flow ahead of an approaching shortwave will shift the deeper moisture and focus for heavier precipitation farther to the north into Northern California on Sunday into early Monday. Snow levels will remain fairly high, confining the threat for heavy accumulations to the higher elevations of the Shasta Cascade region and the northern Sierra. Meanwhile, the threat for locally heavy, high elevation snow is expected to return to the Olympics and the northern Cascades as an amplified trough approaches the region Monday morning. ...Great Lakes, & Northern Mid-Atlantic... Day 1... A shortwave trough lifting into the Great Lakes this morning will continue to amplify, with a closed low expected to develop and move east from the Lakes into the northern Mid Atlantic later today. Surface low pressure will continue to organize and move northeast through the Ohio Valley with slushy, wet snow likely to develop to its north as it moves into the upper Ohio Valley and lower Great Lakes region later today. WPC guidance shows high probabilities for snow accumulations of 4 inches or more extending from the central and eastern shores of Lakes Erie to the Poconos and Catskills today. By early Saturday, models show the low over the northern Mid Atlantic weakening as energy transfers to a low developing offshore. An inverted surface trough extending northeast from new low may contribute to some additional snows across northeastern Pennsylvania and Upstate New York into early Saturday. ...Northern Plains to Upper Midwest... Days 1-3... As the previously noted low begins to move east of the northern Rockies, heavy snow is expected to develop quickly across portions of northeastern Montana late today before shifting east across North Dakota and into the Red River Valley overnight into early Saturday. Strong forcing aloft, combined with low level warm air advection and frontogenesis will contribute to a swath a moderate to heavy snow progressing steadily east across the region. In addition to the heavy snow, strong gusty winds are likely to contribute to hazardous travel conditions. WPC shows high probabilities for storm total amounts exceeding 8 inches from far northeastern Montana across northern North Dakota to the Red River. The system is expected to weaken as it moves across Minnesota on Sunday. While the threat for widespread heavy snow is expected to wane, some additional locally heavy amounts are possible, especially along the north shore of Lake Superior where easterly flow ahead of the low is likely to bolster totals. For days 1-3, the probability of icing greater than 0.1" is less than 10 percent. Pereira ...Key Messages for the March 9-10 (Western U.S.) Winter Storm... --Strong Winter Storm Lasting into Friday: A winter storm will continue to affect the West Coast, and California in particular, through Friday with a burst of heavy precipitation. --Heavy Rain and High Snow Levels Likely: This will be a warm storm system with rain falling on existing snowpack up to 8500 feet. The highest snow levels, heaviest rainfall, and highest rainfall rates are expected in central California. Considerable flooding impacts are possible across portions of the central coast and San Joaquin Valley. --Rain and Snowmelt Will Lead to Flooding: The most significant snowmelt, and overall flooding threat, is expected below 5000 foot elevation, in areas with shallow snowpack. Creeks and streams in the foothills of the Sierra Nevada will be most vulnerable to flooding from rain and snowmelt. --Heavy, Wet Snow at Higher Elevations: Higher elevations in northern California and in the Sierra Nevada will receive a heavy, wet snow. This will lead to difficult travel, and combined with an already deep snowpack, may lead to increasing impacts from the depth and weight of the snow.