Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 403 PM EDT Sat Mar 23 2024 Valid 00Z Sun Mar 24 2024 - 00Z Wed Mar 27 2024 ...Northeast... Day 1... Right-entrance region forcing associated with a strengthening upper jet centered over southeastern Canada will support a deepening surface low that will move north from the northern Mid Atlantic to the New England coast this evening. In addition to the strong upper forcing, increasing low level frontogenesis west of the low track will support moderate to heavy precipitation continuing across portions of New England into the evening. With the cold air locked in, snow will continue across interior New England, with rates increasing up to 2 in/hr across northern Maine. An icy transition zone is expected further south from western Massachusetts to coastal Maine into the evening, before ending as snow as the cold air deepens behind the departing low. Precipitation will taper off from west to east overnight, exiting the region by daybreak as the low tracks quickly into Atlantic Canada. WPC PWPF shows high probabilities (greater than 70 percent) for additional snow accumulations of 6 inches or more covering much of northern Maine this evening. Further south, moderate (greater than 40 percent) to high probabilities for accumulating ice extend from western Massachusetts through portions of southern New Hampshire and coastal Maine. ...The West/Four Corners... Days 1-3... Multi-stream troughing moving into the West will feature an upper low moving into Oregon this evening along with a southern shortwave tied to a 180kt jet moving through SoCal and into the Desert Southwest. Leading surface cold front has already pushed inland, coincident with the height falls, spreading generally light snow over much of the Great Basin toward the central Rockies. The southern shortwave will track across AZ/NM, favoring D1 snowfall over the Mogollon Rim and Utah ranges into especially the San Juans, enhanced by favorable orographic upslope. There, WPC probabilities of at least 6 inches are high (>70%), generally above 7000-8000ft. By D2, surface low pressure will form/organize and deepen over southeastern CO as colder air rushes southward on increasingly northerly flow east of the Rockies. This will turn rain to snow from south to north with snow expanding down the I-25 corridor. Snowfall accumulations will generally be a few inches, with the highest probabilities for at least 4 inches (>50%) above 6000ft, including the Sangre de Cristos to the Raton Mesa. Snowfall will linger into D3, primarily over northeastern NM where a few inches are likely. The northern stream upper low this evening will weaken into an open wave and dive SSE through NorCal, helping to maintain snowfall into the Sierra D1 (along with the northern extent of the southern stream shortwave). WPC probabilities for at least 6 inches of snow are >50% above about 5000ft. Farther north, another system into the Pac NW will bring in several inches of snow to the Cascades, esp D2-3 and above 5000-5500ft. ...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 Next Week** Height falls out of the Rockies will help spur cyclogenesis in southeastern CO by Sunday morning as the upper jet starts to amplify along 105W. Easterly upslope will persist over much of MT and back toward northeasterly to northerly flow, promoting modest to occasionally heavier snow over eastern areas as minor shortwaves punch through and weaken the upper ridge axis. By Sunday afternoon, low pressure will start to trek out of SE CO into SW KS with southerly flow increasing over the Plains on 850mb winds of 50kts. WAA-driven snow (and/or a mixture of sleet/freezing rain) north of a forming surface boundary will expand across the central Plains to the Upper Midwest, with heavier snow into MN. Icing potential will be highest over SD/NE D1 where a few hundredths to a tenth of an inch of ice is possible. On D2, low pressure will lift into Iowa as the upper pattern amplifies, surging warmer and more moisture- laden air northward, changing snow to rain from south to north over Iowa into southern MN. Highest snowfall totals will be transient, and generally north of the warm front near the best dynamics and mid- level FGEN. However, northeast of the low pressure, the rain/snow line will lift northward toward/into Lake Superior while areas on the northwest side of the low will lie near the pivot point in the flow, resulting in a maximum in snowfall -- likely over northeastern SD (Coteau des Prairies) and across central MN. Snowfall rates will likely exceed 1"/hr with increasingly wind conditions, resulting in areas of blowing and drifting snow. Into the MN Arrowhead, warm surge may slow its northward progression, allowing colder northeasterly flow to persist over land with easterly flow across the lake, enhancing snow totals near and northeast of Duluth (assuming the column can stay below freezing). By D3, the surface low will continue northeastward toward the Bayfield Peninsula/far western U.P. of Michigan, with additional snow northwest of the low across north central MN. Snow will eventually wind down by the end of the period (Tues evening) as the low pulls into Ontario. For more details on impacts, please review our latest Key Messages below. Fracasso/Pereira ***Key Messages for Northern Plains Winter Storm*** --A high-impact winter storm developing An extensive system will continue to develop today, producing widespread heavy snow and gusty winds that will persist over parts of the Northern Plains and Upper Midwest through early next week. --Widespread heavy snow expected Heavy snow will spread across much of central and eastern Montana by tonight, expand into the Northern Plains and Upper Midwest on Sunday, and continue into Tuesday. There is a high chance (>70%) of at least eight inches of snow extending from central South Dakota northeastward to northeastern 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. Hazardous travel and road closures are expected late today into early next week. 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.