Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 411 AM EDT Sun Mar 24 2024 Valid 12Z Sun Mar 24 2024 - 12Z Wed Mar 27 2024 ...The West/Four Corners... Days 1-3... A longwave trough encompassing most of the western U.S. will continue to produce rounds of heavy mountains snow today and into early Monday morning. While snow will be winding down in California throughout the day on Sunday, a vigorous 500mb vorticity max moving through the Four Corners region will induce PVA aloft and stream a plume of 850-500mb moisture flux into the Mogollon Rim, the Gila Mountains, the Wasatch, the Colorado Rockies, and both the Sangre De Cristo and San Juans of northern New Mexico. Snowfall rates will be heaviest in the Colorado and New Mexico Rockies where higher elevations >8,000ft will witness the best upslope enhancement. WPC PWPF shows high chances (>70%) for snowfall totals >8" in most of the Colorado and northern New Mexico Rockies, while probabilities are closer to moderate levels (40-60%) in the tallest peaks of the Wasatch, Mogollon Rim, and Gila Mountains. The WSSI shows Minor to Moderate Impacts throughout all these ranges through Sunday night, with the Gila and San Juans sporting some localized Major Impacts at their crests. Snow will gradually wind down Monday morning as the best upper level support moves east into the Plains, but some residual Pacific moisture throughout the West may result in localized moderate-to-heavy snow showers along the Rockies and as far west as the Great Basin. Meanwhile, a persistent onshore flow in the Pacific Northwest will produce some snow in the Cascades and Olympics on Monday, but snowfall rates will be manageable for these ranges. This may all change by Wednesday as the next Pacific storm system approaches the Washington coast with a renewed influx of Pacific moisture on its way that may bring more heavy snow to the Olympics, Cascades, and as far south as the Sierra Nevada. ...Northern Rockies & High Plains, Central Rockies, Upper Midwest... Days 1-3... **Major Winter Storm to Impact Northern High Plains to the Upper Midwest into Early This Week** This morning, a deepening surface low in eastern Colorado and a deepening 700mb low over western Nebraska will funnel copious amounts of Gulf of Mexico moisture northward into the Northern Plains and Upper Midwest. A deformation axis of snow will take shape over eastern Montana, northern Wyoming, and the Dakotas, while strong 850-700mb WAA generates thumping snow rates from northern Iowa and southern Minnesota to western Wisconsin. Latest WPC Snowband Probability Tracker (SPT) does depict snow bands that will likely produce 1-2"/hr snowfall rates late Sunday morning and into Sunday afternoon, with some cases where as high as 3"/hr are possible. As Sunday unfolds the Central Plains will located beneath the divergent left-exit region of a 250mb jet streak in northern Mexico, while the right-entrance region of a 250mb jet streak over southern Ontario maximizes the intense vertical ascent atop the atmosphere. This allows for the surface low in the Central Plains to drop to exceptionally deep levels (sub-980mb by Sunday evening). On the backside of the deepening 700mb low, strong northeasterly upslope flow and a potent cold front will allow for heavy snow to break out along the Front Range of the Colorado Rockies and the Palmer Divide Sunday evening, followed by the Sangre De Cristo and as far south as Raton Pass Sunday night into early Monday morning. Latest WPC SPT shows some instances where 2-3"/hr snowfall rates may ensue with concerns of rapid snow accumulation on roads and significantly reduced visibilities into early Monday morning. Similar snowfall rates may occur in west- central Nebraska and northwest Kansas as the warm conveyor belt wraps around the northwest flank of the low. The ascent is so strong at low-mid levels that instances of thundersnow are possible Sunday night into Monday morning in some localized cases. Monday morning will see the storm system track northeast towards eastern Nebraska with strong 850mb WAA in the Upper Mississippi Valley ultimately causing a change over from snow to an icy wintry mix at first, then to all rain in southern Minnesota, northern Wisconsin, and the U.P. of Michigan by Monday afternoon. This will cut down snowfall totals but the icy wintry mix of sleet and freezing rain could still lead to hazardous travel conditions Monday morning. Meanwhile, in the eastern Dakotas and northern Minnesota, snow will remain the primary precip type with strong wind gusts >40 mph causing blizzard conditions through Monday evening. The expansive deformation axis of snow will pivot over these areas Monday night with snow also falling through eastern Nebraska and northern Kansas. By Tuesday morning, the storm will be over the Upper Mississippi Valley with the swath of heavy snow traversing much of Minnesota and the Upper Missouri river Valley. Snow will finally taper off from southwest to northeast Tuesday afternoon and be well into southern Canada by early Wednesday morning. The latest WSSI shows Major impacts in northeastern South Dakota, southeastern North Dakota, much of central Minnesota, and the Minnesota Arrowhead. These areas also sports high chances (>70%) for snowfall totals >12" for the duration of this winter storm. There are even low-to-moderate chances (30-50%) for >18" in northeast South Dakota and along the coast of the Minnesota Arrowhead. WPC PWPF also depicts high chances (>70%) for snowfall totals >8" in northern Nebraska, central South Dakota, and northwest Wisconsin. West-central Nebraska features moderate-to- high chances (50-70%) for >6" of snow to go along with whipping wind gusts surpassing 45 mph. Farther south, the Colorado Front Range, Palmer Divide, and Sangre De Cristo have moderate-to-high chances (50-70%) for >6" of snowfall through Monday morning. Expect hazardous travel in these affected areas Sunday and through Monday with blowing and drifting snow causing higher snow drifts and significantly reduced visibilities. Mullinax ***Key Messages for Northern Plains Winter Storm*** --A high-impact winter storm unfolding An extensive storm system will continue to develop today, producing widespread heavy snow and gusty winds that will persist over parts of the Northern Plains and Central Plains as well as Upper Midwest through early this week. --Widespread heavy snow expected Heavy snow will expand into the Northern Plains and Upper Midwest today and continue into Tuesday. Heavy snow is also expected in parts of the Central Plains Sunday night into Monday. There is a high chance (>70%) of at least eight inches of snow extending from northern Nebraska and central South Dakota northeastward to central Minnesota and northwestern Wisconsin. --Hazardous impacts due to snow, snow load, and wind Heavy snow and gusty winds will produce areas of blowing and drifting snow and possible blizzard conditions Sunday into Monday. This will result in hazardous travel including road closures. Strong winds and heavy, wet snow on trees and power lines may damage trees and cause power outages. --Strong wind gusts in the Central and Southern Plains Wind gusts over 50 mph on Sunday may result in power outages, blowing dust with reduced visibility, difficult travel, and property damage. Critical fire weather conditions are forecast today over the Southern High Plains.