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   FOUS11 KWBC 120808   
   QPFHSD   
      
   Probabilistic Heavy Snow and Icing Discussion   
   NWS Weather Prediction Center College Park MD   
   308 AM EST Mon Jan 12 2026   
      
   Valid 12Z Mon Jan 12 2026 - 12Z Thu Jan 15 2026   
      
      
   ...Great Lakes...   
   Days 1-3...   
      
   Ongoing westerly flow over Lake Ontario will keep additional heavy   
   snowfall of 6-12" in the forecast today over the Tug Hill Plateau,   
   while minor amounts generally between 1-4" occurs around the   
   Buffalo area and the Adirondacks. By tonight, a Canadian clipper   
   system will race east over southern Ontario with just enough low-   
   level WAA and a plume of 700-300mb moisture aloft to support a   
   brief overrunning setup over the MN Arrowhead, northern WI, and the   
   western MI U.P.. Ice accumulations are likely to be less than a   
   tenth of an inch, but WPC probabilities show moderate chances   
   (>50%) for ice accumulations over on-ehundreth of an inch. Slick   
   spots on untreated surfaces are possible Monday night and into   
   Tuesday morning in affected areas.   
      
   As the clipper continues to advance east into southeast Canada, a   
   robust 500mb vorticity max diving south will accompany a strong   
   cold front that induces strong CAA over Lake Superior Tuesday   
   night. Snow will increase in intensity over the Michigan U.P. as   
   surface-850mb delta Ts dramatically increase and low-level lapse   
   rates sharpen. The upper-level trough continues to dive south   
   through the Great Lakes on Wednesday and the same CAA regime will   
   race south over Lake Michigan. Guidance is coming into better   
   agreement on the formation of a potent single-band LES setup   
   producing a swath of heavy snow over northwest IN that could   
   oscillate at times to as far west as the WI/IL lake shores and as   
   far east as southwest MI. Meanwhile, much of Michigan's Mitten will   
   contend with multi-band lake effect streamers as a surface trough   
   pivots over the Great Lakes Wednesday and into Wednesday night.   
   This same trough axis, along with the CAA over the Great Lakes,   
   will trigger lake-enhanced snowfall over northern OH, northwest PA,   
   and western NY by early Thursday morning. Snowfall will become   
   more synoptically-enhanced by early Thursday morning as a 700mb low   
   tracks over Lake Erie and would support heavy snowfall into the   
   day on Thursday as well.   
      
   24-hour WPC probabilities through 12Z Wednesday show   
   moderate chances (40-60%) for snowfall totals >6" along the   
   Keweenaw Peninsula and both the Huron and Porcupine Mountains of   
   the MI U.P.. 24-hour probabilities through 12Z Thursday depict   
   northwest IN as having moderate chances (40-60%) for snowfall   
   totals >6". Note that should 1-2"/hr rates materialize, localized   
   amounts approaching a foot of snow are possible. Lastly, through   
   12z Thursday, the first 6-12 hours of the impending winter storm   
   show low chances (10-30%) for snowfall totals >4", but with the   
   storm likely to produce additional heavy snow along the Chautauqua   
   Ridge and into western NY, expect heavier snowfall totals to   
   envelop these areas through Thursday. The WSSI-P currently shows   
   moderate-to-high chances (50-70%) for at least Minor Impacts over   
   northwest IN, northeast OH, and western NY through Thursday   
   morning.   
      
   ...Upper Ohio Valley, Central Appalachians, & Northeast...   
   Days 3-3.5...   
      
   A robust 500mb shortwave trough over the Upper Midwest will race   
   southeast toward the Ohio Valley Wednesday night. There remains a   
   fair amount of uncertainty and model spread that is making this   
   forecast tough in the Ohio Valley and as far east as the I-95   
   corridor, but the higher confidence areas are the spine of the   
   Appalachians. As the 500mb shortwave deepens into a closed upper   
   low Wednesday night, an accompanying strong cold front will   
   collide with the central Appalachians with strong 925-700mb layer   
   CAA. The combination of brisk NWrly flow and excellent PVA aloft   
   ahead of the upper low will produce heavy snowfall rates from the   
   Laurel Highlands of southern PA on south to the Blue Ridge and   
   Smokey Mountains. Snow is likely to continue beyond the scope of   
   this short-term discussion as cyclonic flow around the western   
   flank of the storm system sustains favorable upslope flow into the   
   central Appalachians. The WSSI-P is showing >50% chances for a   
   at least Minor Impacts over the Smokeys of TN/NC, and both the   
   windward slopes and peaks of the central Appalachians. Residents   
   and travelers should plan for a disruptive snow event in central   
   Appalachians Wednesday evening and into Thursday.   
      
   From the Ohio Valley on north through western PA and into the   
   Northeast the forecast is more murky. Guidance across the board   
   shows different evolutions and tracks of the aforementioned 500mb   
   low. The CMC shows a lack of deepening/phasing of 500mb vort   
   maxima that keeps the synoptic-scale forcing limited. The ECMWF/EC-   
   AIFS/UKMET camps show a closed low by tracking across the lower   
   Great Lakes and into the Northeast. To illustrate the ongoing   
   changes, the 00Z ECMWF from 24 hours ago had a closed low south of   
   Louisville, KY by 12Z Thursday, while the latest 00Z ECMWF has the   
   closed low near Cleveland, OH at the same time Thursday. Lastly,   
   the GFS/GEFS is farther south over the OH Valley that then heads   
   for the Mid-Atlantic coast as a weakening closed low. All these   
   evolutions lead to different snowfall footprints, particularly   
   along the I-95 corridor and northern Mid-Atlantic. No matter the   
   track of the upper-low, the meteorology involved supports periods   
   of snow north of the emerging 700mb low. The EPS/GEFS both show the   
   left-exit region of a strengthening jet streak off the southeast   
   coast being placed over the Northeast, which also pairs favorably   
   with 700mb Q-vector convergence on both GFS and ECMWF solutions   
   over the eastern Great Lakes and interior Northeast. Through 12Z   
   Thursday, WPC probabilities show northern OH (including the   
   Cleveland metro) on north and east along the Chautauqua Ridge and   
   the Adirondacks showing low-to-moderate chances (30-50%) for >4" of   
   snowfall.   
      
   Residents and travelers across the Northeast will want to monitor   
   the forecast closely in the coming days as this complex forecast is   
   likely to change in the coming days. The lowest confidence in terms   
   of snowfall amounts and impacts are along the I-95 corridor as   
   potential scenarios range from a significant winter storm for areas   
   along I-95 in southern New England to minor snow accumulations at   
   most depending upon the strength and track of the approaching   
   upper-low. Not only are amounts unclear, but boundary layer   
   temperatures at the onset Wednesday night and early Thursday   
   morning would support rain as the initial precipitation type before   
   changing over to snow. For now, the spine of the Appalachians are   
   favored to see accumulating snowfall late Wednesday into Thursday.   
      
      
   Mullinax   
      
      
      
      
      
   $$   
      
   = = =   
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