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   FOUS11 KWBC 241905   
   QPFHSD   
      
   Probabilistic Heavy Snow and Icing Discussion   
   NWS Weather Prediction Center College Park MD   
   205 PM EST Mon Nov 24 2025   
      
   Valid 00Z Tue Nov 25 2025 - 00Z Fri Nov 28 2025   
      
      
   ...Significant winter storm to impact parts of the Northern Plains   
   and Upper Midwest/Great Lakes through Wednesday before lake effect   
   snow intensifies on Thanksgiving. Key Messages have been issued for   
   this storm...   
      
      
   ...Northern Plains/Upper Midwest/Upper Great Lakes...   
   Days 1-3...   
      
   Shortwave trough exiting the Northern Rockies this afternoon will=20   
   move into the northern High Plains tonight. The upper jet across=20   
   the US/Canada will sharpen and support a strengthening area of low=20   
   pressure that will move from the Plains to the Upper Midwest and=20   
   western Great Lakes over the next few days. Tonight, an 850mb low=20   
   will form along a strengthening 925-850mb front over central ND,=20   
   while a narrow inverted trough axis forms on its western flank. By=20   
   12Z Tuesday, bands of moderate to heavy snow are likely from=20   
   northeastern MT to central ND with increasingly gusty winds as the=20   
   low pressure strengthens. Tuesday afternoon the low over=20   
   southeastern MN will start to deepen even more rapidly as the mid-   
   level shortwave starts to close off, allowing a TROWAL to form on=20   
   the western side of the storm. This could allow for >1"/hr snowfall   
   rates along with gusty winds over 30mph, causing some blowing/drifting   
   snow. Some areas closer to Lake Superior and over central MN will=20   
   see marginal temperatures and snow may not accumulate quickly if=20   
   the rates are not high, though colder air will eventually win and=20   
   change all areas to snow overnight into early Wednesday as the low=20   
   moves into the U.P. of Michigan and deepens into the mid 990s mb.   
   There remains some latitudinal uncertainty with today's guidance   
   shifting slightly south across the ND/MN and aligned with the   
   second ensemble cluster in WPC's QPF cluster prototype in the   
   north-central U.S.. Mesoscale banding within the inverted trough   
   and eventual TROWAL will likely make for rapidly changing   
   conditions within narrow corridors of heavy snow.   
      
   By Wednesday night into early Thursday, the system will reach its=20   
   peak intensity over Ontario and take the bulk of its snow with it.=20   
   However, northerly to northwesterly flow will transition the lake-=20   
   enhanced snow to lake effect snow over northern WI into the U.P.=20   
   where the 850-lake temperature difference will be >15C (-10 to   
   -14C at 850mb and a lake temperature around 5C). Lake effect snow=20   
   will eventually break out across the rest of the Great Lakes by=20   
   Thursday morning and continue into the medium range period.=20   
      
   WPC probabilities for at least 8 inches of snow are 30-50% from=20   
   northwestern ND to central MN. Then, these probs increase to 50-70%   
   across northeast MN and the MN Arrowhead. Across northern WI and=20   
   into the U.P., the combination of synoptic snow and then lake=20   
   effect snow will boost totals well over a foot. There, WPC=20   
   probabilities for at least 24 inches of snow are 50-80% from near=20   
   Ironwood northeastward across the northern portion of the U.P. near   
   the Huron Mountains. This region is also where major impacts due to   
   snow amounts are possible. Residents and visitors in the Upper   
   Midwest/Great Lakes are advised to check the latest forecast=20   
   before traveling this week.   
      
      
   ...Great Lakes...   
   Day 3...   
      
   Lake effect snow will continue on day 3 (00z 11/27-00z 11/28) as   
   the deep low drifts into southeast Canada and promotes strong   
   west-northwesterly flow over the relatively warm lake waters. Fetch   
   will be favorable for additional snow across the U.P. of MI and the   
   northern L.P., as well as along the shores of Lake Erie from   
   northwest PA to western NY as well as the Tug Hill of NY downwind   
   of Lake Ontario. Current WPC probabilities for at least 8 inches of   
   snow on day 3 are 60-80% for these locations.   
      
   ...Pacific Northwest/Northern Rockies...   
   Days 1-3...   
      
   The next Pacific system moves into western WA on Tuesday at the=20   
   nose of an 140kt 250mb jet. Colder air in place ahead of the=20   
   moisture may support some spotty freezing rain along the leeward=20   
   slopes/valleys of the Cascades and in the valleys of the Columbia=20   
   River Basin over northern WA. Snow levels will gradually rise as=20   
   the warm front lifts through Tuesday night into early Wednesday,=20   
   but the surface front will takes longer to cross the Cascades=20   
   rather than the more robust 700mb WAA nose that support the=20   
   potential for icy conditions east of the Cascades. Thanks to a=20   
   longwave trough firmly entrenched over the North Pacific, an=20   
   extended moisture fetch into the the Pacific Northwest will support   
   a more or less continuous stretch of mountain snow over the=20   
   Cascades and downstream into the Northern Rockies through the end=20   
   of this forecast period (then continuing into the medium range).=20   
   Snow levels will vary, starting around 2000-4000ft then rising to=20   
   around 5000-7000ft as milder air moves in ahead of a potent low   
   pressure system on Thursday. WPC probabilities for at least 8=20   
   inches of snow are >50% above about 5000ft. Both Snoqualmie and=20   
   Stevens Pass may see multiple inches of snow before snow levels=20   
   rise above the passes early Wednesday.   
      
      
   The probability of significant ice across the CONUS is less than=20   
   10 percent.   
      
   Snell   
      
      
   ...Winter Storm Key Messages are in effect. Please see current=20   
    Key Messages below...   
      
   https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late=   
   stKeyMessage_1.png__;!!DZ3fjg!_60s3P1rZA2qOM-sH8hmxQmMcm_TMHKSclFZitwZibDbR=   
   9U43WW4a4OnOF9smZ5yJhTQx51PqToOcrM8C9y7zFDOnTw$=20   
      
      
      
   $$   
      
   =3D =3D =3D   
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