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   Probabilistic Heavy Snow and Icing Discussion   
   NWS Weather Prediction Center College Park MD   
   325 AM EST Wed Dec 10 2025   
      
   Valid 12Z Wed Dec 10 2025 - 12Z Sat Dec 13 2025   
      
      
   ...Pacific Northwest through the Northern High Plains...   
   Days 1-3...   
      
   The atmospheric river (AR) plaguing the Pacific Northwest with   
   copious amounts of rainfall continues today and into Thursday with   
   anomalous Pacific moisture coupled with >90th climatological   
   percentile winds within the 700-200mb layer over WA, northern ID,   
   and much of MT. Snow levels will be on the rise today, reaching   
   anywhere from 7,000-9,000ft as the 500-200mb jet core drifts north.   
   This should begin to force most passes to changeover to rain,   
   while any lingering snow occurs in the more remote areas of the   
   Cascades and Lewis Range. The only notable area for heavy snowfall   
   today is along the >9,000ft peaks of the Absaroka, Tetons, Big   
   Horns, and Wind River ranges of southern MT and western/northern   
   WY. WPC probabilities show moderate-to-high chanceS (50-70%) for   
   snowfall totals >8" through Wednesday night.   
      
   Focus turns to Thursday as an Alberta Clipper tracking across   
   eastern MT helps to usher in an Arctic front from southern Canada.   
   As the Arctic high builds in from the north, low-level easterlies   
   will upslope into central and western MT at the same time a ribbon   
   of 700-300mb moisture streams in overhead. 700mb WAA within W-NW   
   flow will encounter the Arctic air-mass and result in a band of   
   700mb FGEN over central MT by Thursday night, resulting in a   
   quasi-stationary zone of heavy snow over the heart of Big Sky   
   Country. Heavy snow will linger over the heart of MT through Friday   
   afternoon before drifting east into eastern MT and the western   
   Dakotas Friday night. As the band advances east, downsloping winds   
   and a drying within the 800-500mb layer could cause precipitation   
   to change over to a wintry mix in central MT, potentially   
   resulting in a glaze of ice atop fresh snow Friday night.   
      
   WPC probabilities moderate-to-high chances (50-80%) for snowfall   
   totals >8" in central MT with even some low-chance probabilities   
   10-30%) for isolated totals surpassing 18". The Lewis Range above   
   5,000ft are likely to receive anywhere between 12-24" of snowfall,   
   with the remote reaches of the Big Snowy and Little Belt Mountains   
   potentially exceeding 24". The WSSI-P Moderate probabilities in   
   central MT are >50% in central and south-central MT, with   
   Interstates 90, 94, and 87 all at risk of seeing hazardous travel   
   conditions, with some potential for considerable disruptions and   
   closures as well. This is depicted in the WSSI-P as well,   
   indicating 10-20% chances for Major Impacts along portions of these   
   Interstates Friday and into Saturday morning.   
      
      
   ...Great Lakes & Northeast...   
   Days 1-3...   
      
   A shortwave trough responsible for the heavy snow across portions   
   of the Upper Midwest will strengthen as it tracks through the OH   
   Valley today. As it does, strong WAA out ahead of the trough will   
   work in tandem with the left-exit region of a 250-500mb mean   
   layered left-exit region over the Northeast to produce widespread   
   precipitation today from the central Appalachians to New England.   
   An exceptionally cold/dry antecedent air-mass by early December   
   standards will keep wet-bulb temperatures cold enough to support   
   snow at the onset across northern PA, the Catskills, Tug Hill,   
   Adirondacks, Berkshires, and the rest of the New England mountains   
   through Wednesday afternoon. Farther south, central and eastern   
   PA, as well as northwest NJ, are likely to see an icy wintry mix   
   this morning that could result in slick roads, particularly after   
   following a couple very chilly days where surfaces have been   
   steadily below freezing. From this "front-end thump" of WAA-driven   
   and some upslope enhanced snowfall, snowfall totals are likely to   
   range mostly between 1-4" with the higher totals confined to the   
   Tug Hill, Adirondacks, Berkshires, Green, and White Mountains where   
   WPC probabilities show high chances (>70%) for snowfall totals >6"   
   through Wednesday night.   
      
   As low pressure tracks into the St. Lawrence Valley tonight, CAA   
   within cyclonic flow on the backside of the storm will kick-start   
   the Lake Effect Snow (LES) machine, as well as supply the central   
   Appalachians with pronounced upslope snowfall. Precipitation will   
   fall as snow across the Central Appalachians with lowering snow   
   levels throughout the day Wednesday and impressive 40-50 kts winds   
   at 850mb will mix down to cause strong winds within increasing   
   snowfall rates. This will result in dangerous travel conditions in   
   the Central Appalachians with whiteout conditions expected above   
   2,000ft. Snow and winds should gradually taper off Thursday   
   morning. WPC probabilities show moderate-to-high chances (50-70%)   
   for snowfall totals >6" with localized low-chance probabilities   
   (10-30%) for amounts >12". Elsewhere, the LES belts over the   
   eastern Michigan U.P., northwest section of Michigan's Mitten,   
   along the Chautauqua Ride, and down wind of Lake Ontario will see   
   LES bands that stick around these areas through Thursday, with the   
   band off of Lake Ontario lingering into Friday as well. Through   
   Friday morning, the Tug Hill Plateau sports high chances (>70%) for   
   snowfall totals topping 12", with moderate-to-high chances (40-70%)   
   for >12" amounts along the Chautauqua Ridge through Friday   
   morning.   
      
      
   ...Northern Plains, Midwest, Lower Ohio Valley, & Central   
   Appalachians...   
   Days 2-3...   
      
   A potent clipper emerging from eastern MT Thursday morning will   
   race southeast into the heart of the Midwest by Thursday evening.   
   Healthy 850mb WAA and FGEN to the north and east of the low track   
   will cause a narrow band of snow light-to-moderate snow from the   
   eastern Dakotas and southern MN to the nose of IA, and in some   
   cases a wintry mix across the northern High Plains. The 850mb   
   FGEN/WAA pivots over the Lower Ohio Valley Thursday night and   
   reaches the Central Appalachians by early Friday morning. WPC   
   probabilities show generally lw-to-moderate chances (20-50%) for   
   >4" of snow from central MN on south and east across northern IL,   
   south-central IN, and southern OH. The highest probabilistic   
   chances for >4" of snowfall resides in the Potomac Highlands and   
   central Appalachians of eastern WV and western MD. Here, WNWrly   
   upslope winds within a 290K isentropic regime and higher SLRs will   
   provide a favorable environment for locally heavy snowfall. WPC   
   probabilities show most of the Potomac Highland and central   
   Appalachians in eastern WV and western MD have moderate-to-high   
   chances (50-70%) for snowfall totals >4", with some guidance   
   indicating low chances (10-30%) for localized totals surpassing   
   10".   
      
   There are some members of guidance that depict a chance for light   
   snowfall across the Mid-Atlantic on Friday, particularly the Blue   
   Ridge of VA/WV and potentially in the northern VA/northern   
   MD/southern PA. ECMWF and GFS show weak 700mb Q-vector convergence   
   over the region with just enough 700-300mb layer saturation to   
   support a chance for light snow. WPC probabilities show low chances   
   (10-30%) for >1" snowfall totals across southern and central PA,   
   northern MD, and northwest VA. While referencing >1" snowfall   
   potential may seem trivial to mention, recent Mid-Atlantic   
   snowfall events over the past week has seen snowier trends inside   
   of 60 hours. It is worth monitoring, but overall snowfall and   
   travel disruption potential at this time would be light. The WSSI-P   
   does show 10-20% odds for Minor Impacts across portions of northern   
   VA and northern MD on Friday.   
      
      
   Mullinax   
      
      
      
      
   $$   
      
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