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   FOUS11 KWBC 132020   
   QPFHSD   
      
   Probabilistic Heavy Snow and Icing Discussion   
   NWS Weather Prediction Center College Park MD   
   320 PM EST Tue Jan 13 2026   
      
   Valid 00Z Wed Jan 14 2026 - 00Z Sat Jan 17 2026   
      
      
   ...Northern Plains through the Northeast, and the Appalachians...   
   Days 1-3...   
      
   A trough across the eastern CONUS will amplify impressively and   
   periodically re-load through the period as repeated shortwaves   
   intensify and drop southeast from Canada. The core of this trough   
   will deepen most impressively to reach the Gulf Coast Thursday aftn   
   (NAEFS 500mb heights below the 1st percentile within the CFSR   
   climatology), but remain below the 10th percentile with secondary   
   amplification occurring on Friday.   
      
   Within this trough, and really the driving factor behind amplifying   
   this trough, will be repeating shortwaves digging out of Canada and   
   racing southeast through the flow. The first of these will move   
   from Minnesota to the Ohio Valley D1, with a secondary piece   
   approaching the Gulf Coast, with both of these impulses rotating   
   eastward during D2, producing the most intense troughing on   
   Thursday. Within this progressive flow, even as these lead impulses   
   rotate away on Friday, the next vorticity lobe will follow   
   immediately in its wake, moving from the Northern Plains to the   
   Mid-Mississippi Valley on D3.   
      
   This pattern will produce multiple days of lake effect snow (LES)   
   downwind of the Great Lakes, especially in the more northerly belts   
   as winds become NNW beneath strong CAA. 3-day WPC probabilities for   
   LES are high (>70%) for more than 8 inches in the higher elevations   
   of the U.P. including the Huron and Porcupine Mountains, as well as   
   along the E/SE shore of Lake Michigan into northern Indiana, and   
   across the Tug Hill Plateau, with lower but still significant   
   probabilities (30-50%) for 8+ inches along the Chautauqua Ridge.   
   The heaviest LES is likely in a single band off Lake Michigan into   
   SW MI/NW IN late Wednesday through late Thursday.   
      
   Across the Central Appalachians and Northeast, the lead shortwave   
   will not only work together with an Atlantic-offshore jet streak to   
   create low pressure development across the Northeast, but also drag   
   an arctic front from the Ohio Valley through the Mid-Atlantic on   
   Thursday. This will create a short period of heavy upslope snow   
   from the higher elevations of NC through the Laurel Highlands of PA   
   where WPC probabilities are moderate (50-70%) for at least 4   
   inches, generally above 3000 ft, with locally 6-8 inches possible.   
   Farther north into Upstate NY and northern New England, a weak   
   TROWAL may pivot westward north of the surface low and combine with   
   an inverted surface trough to enhance snowfall D2. Trends in the   
   guidance continue to shift the heaviest snowfall north into Canada,   
   but a narrow corridor of heavy snow is likely, reflected by WPC   
   probabilities for 6+ inches that are 50-70% from eastern Lake   
   Ontario (where some lake enhancement is likely) through the St.   
   Lawrence Valley and the Adirondacks.   
      
   Finally, on D3 with the next shortwave digging out of Saskatchewan   
   into the Upper Midwest, height falls and modest warm/moist   
   advection will create a swath of generally light snow, followed by   
   strong winds behind yet another arctic front. WPC probabilities   
   indicate only a 10-30% chance for at least 4 inches of snow for   
   parts of SD/MN/WI, but WSSI-P suggests an increasing threat for   
   blowing snow impacts just behind this wave, so travelers should be   
   prepared for hazardous driving Friday despite the modest snowfall   
   amounts forecast.   
      
      
   Weiss   
      
      
   $$   
      
   = = =   
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