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   FOUS11 KWBC 240813   
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   Probabilistic Heavy Snow and Icing Discussion   
   NWS Weather Prediction Center College Park MD   
   313 AM EST Mon Nov 24 2025   
      
   Valid 12Z Mon Nov 24 2025 - 12Z Thu Nov 27 2025   
      
      
   ...Northern Rockies...   
   Day 1...   
      
   Shortwave over Washington this morning will carry a cold front   
   through the Northern Rockies today. The strongest height falls will   
   cross through northwestern MT around Glacier NP with modest snow   
   above 5000-6000ft. WIth the moisture feed stretched back (but   
   weakening) to the Pacific, snow will fall as far south as the   
   Bitterroots and into northwestern WY where amounts will be lower (a   
   few inches). Snow will taper from west to east this afternoon   
   through this evening as the cold front makes steady progress   
   through the region. WPC probabilities for at least 8 inches of snow   
   are >50% above about 5000ft.   
      
      
   ...Pacific Northwest/Northern Rockies...   
   Days 2-3...   
      
   The next Pacific system moves into western WA on Tuesday at the   
   nose of an 140kt 250mb jet. Colder air in place ahead of the   
   moisture may support some spotty freezing rain along the leeward   
   slopes/valleys of the Cascades and in the valleys of the Columbia   
   River Basin over northern WA. Snow levels will gradually rise as   
   the warm front lifts through Tuesday night into early Wednesday,   
   but the surface front will takes longer to cross the Cascades   
   rather than the more robust 700mb WAA nose that support the   
   potential for icy conditions east of the Cascades. Thanks to a   
   longwave trough firmly entrenched over the North Pacific, an   
   extended moisture fetch into the the Pacific Northwest will support   
   a more or less continuous stretch of mountain snow over the   
   Cascades and downstream into the Northern Rockies through the end   
   of this forecast period (then continuing into the medium range).   
   Snow levels will vary, starting around 2000-4000ft then rising to   
   around 5000-7000ft as milder air moves in. WPC probabilities for at   
   least 8 inches of snow are >50% above about 5000ft. Both   
   Snoqualmie and Stevens Pass may see multiple inches of snow before   
   snow levels rise above the passes early Wednesday.   
      
   ...Northern Plains/Upper Midwest/Upper Great Lakes...   
   Days 1-3...   
      
   The shortwave trough exiting the Northern Rockies this afternoon   
   will move into the northern High Plains tonight. The upper jet   
   across the US/Canada will sharpen and support a strengthening area   
   of low pressure that will move from the Plains to the Upper Midwest   
   and western Great Lakes over the next few days. Tonight, an 850mb   
   low will form along a strengthening 925-850mb front over central   
   ND, while a narrow inverted trough axis forms on its western flank.   
   By 12Z Tuesday, bands of moderate to heavy snow are likely from   
   northeastern MT to central ND with increasingly gusty winds as the   
   low pressure strengthens. Tuesday afternoon the low over   
   southeastern MN will start to deepen quickly as the mid-level   
   shortwave starts to close off, allowing a TROWAL to form on the   
   western side of the storm. This could allow for >1"/hr snowfall   
   rates along with gusty winds over 30mph, causing blowing/drifting   
   snow. Some areas closer to Lake Superior and over central MN will   
   see marginal temperatures and snow may not accumulate quickly if   
   the rates are not high, though colder air will eventually win and   
   change all areas to snow overnight into early Wednesday as the low   
   moves into the U.P. of Michigan and deepens into the mid 990s mb.   
   By Wednesday night into early Thursday, the system will reach its   
   peak intensity over Ontario and take the bulk of its snow with it.   
   However, northerly to northwesterly flow will transition the lake-   
   enhanced snow to lake effect snow over northern WI into the U.P.   
   where the 850-lake temperature difference will be >15C (-10 to -14C   
   at 850mb and a lake temperature around 5C). Lake effect snow will   
   eventually break out across the rest of the Great Lakes by Thursday   
   morning and continue into the medium range period.   
      
   WPC probabilities for at least 4 inches of snow are >50% from   
   northwestern ND to central MN then eastward through the Arrowhead,   
   northern WI, and across much of the U.P. of Michigan. Within this   
   areas, probabilities for at least 8 inches of snow are >50% over   
   northeastern MN due to the synoptic system itself. Across northern   
   WI and into the U.P., the combination of synoptic snow and then   
   lake effect snow will boost totals well over a foot. There, WPC   
   probabilities for at least 18 inches of snow are >50% from near   
   Ironwood northeastward across the northern portion of the U.P. near   
   the Huron Mountains.   
      
   The probability of significant ice across the CONUS is less than   
   10 percent.   
      
   Fracasso   
      
   $$   
      
   = = =   
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