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   FOUS11 KWBC 061854   
   QPFHSD   
      
   Probabilistic Heavy Snow and Icing Discussion   
   NWS Weather Prediction Center College Park MD   
   154 PM EST Sat Dec 6 2025   
      
   Valid 00Z Sun Dec 07 2025 - 00Z Wed Dec 10 2025   
      
      
   ...Pacific Northwest & Northern Rockies...   
   Days 1-3...   
      
   The Pacific Northwest and Northern Rockies will continue to contend   
   with the lingering snow during the D1 period as a shortwave tracks   
   across the region over a broad western U.S. ridge ahead of a strong   
   atmospheric river (AR) set to surge into WA/OR on D2, with lowering   
   snow levels across the Cascades on D3. Snow levels largely start   
   out low around 3,000-4,000 ft, but rapidly rise across the Pacific   
   Northwest on Sunday above 5,000 ft and as the strong AR approaches   
   on Monday these values increase to above 6,000 ft in the northern   
   WA Cascades and above 7,000 ft from Mt. Rainer southward.   
   Meanwhile, snow levels also rise across the northern Rockies to   
   above 5,000-6,000 ft as well before dropping on D3 as the AR ends   
   and the associated shortwave ejects into the northern Plains. For   
   the 72-hr period ending 00z 12/10, WPC probabilities for more than   
   12 inches are high (70-90%) across the WA Cascades above 6,000 ft,   
   as well as parts of the northern Rockies in ID, northwest MT, and   
   northwest WY above 6,000-7,000 ft.   
      
      
   ...Midwest/Great Lakes/Northeast...   
   Days 1-3...   
      
   Fast-moving clipper system currently impacting parts of the   
   northern Plains and Midwest with heavy snow this afternoon will   
   swing across IA/northern IL/southern WI tonight into early Sunday   
   and produce a storm total swath of up to 4-8 inches of fresh   
   snowfall. Height falls ahead of an approaching 500mb vorticity   
   maximum will coincide with the divergent left-exit region of a   
   250mb jet streak to support the developing low pressure system. A   
   strengthening 850mb LLJ will direct a surge of WAA in the 850-700mb   
   layer ahead of the 850mb low. Combined with a healthy 290K   
   isentropic ascent amid SWrly flow, and a moistening DGZ will ensue   
   over northern IA this evening and periods of heavy snow will   
   develop. Snowfall rates may briefly exceed 1"/hr within this east-   
   west corridor just north of the 850mb FGEN extending from northern   
   IA into southern WI/northern IL. However, the 850mb low will begin   
   to quickly weaken tonight, taking on a positive tilt and becoming   
   an open wave. Light- to- moderate snow is expected through Sunday   
   morning into northern IN and the southern L.P. of MI.   
      
   WPC probabilities beginning at 00z Sunday show eastern IA to   
   northern IL (including the Chicago metro) as having the highest   
   chances (40-80%) for snowfall totals more than 4 inches. It is   
   worth noting bitterly cold temperatures will follow in wake of this   
   system Saturday night and through Sunday. By Sunday morning,   
   temperatures will be in the single digits across much of the   
   Midwest and lows below zero Sunday night. Any snow that falls will   
   likely stick around for a couple days, resulting in daily   
   recurrences of icy roads and the potential for black ice.   
      
   This system along with another upper level disturbance by D3 tracking   
   across the Great Lakes and into the Northeast will cause both LES   
   bands and some synoptically- forced snow across these regions   
   Sunday and into early next week. Some LES streamers off Lakes   
   Superior, Erie, and Ontario will keep accumulating snow in the   
   forecast in the usual snow belts of Michigan's U.P., the "Tip of   
   the Mitt" in Michigan, and across western NY. By Sunday morning the   
   upper trough responsible for the Midwest storm on Saturday will   
   make its way through these regions with light-to- moderate snowfall   
   across Michigan and much of the Northeast (minus the I-95 corridor   
   megalopolis). Most snowfall totals will range between 1-4",   
   although some of the LES belts may manage to see some snowfall   
   totals eclipse 4" on Sunday. Lastly, while high pressure builds in   
   over the Northeast on Monday, an Alberta Clipper makes its way   
   toward the Upper Great Lakes by Monday evening with more light-to-   
   moderate snow expected. Strong southerly flow ahead of this system   
   may actually produce a band of heavy lake effect snow oriented from   
   Lake Michigan aimed northward into the eastern U.P.   
      
   WPC probabilities over through Tuesday show moderate-to-high   
   chances (50-80%) for snowfall totals >4" in the typical LES belts   
   of Michigan's U.P., northern Michigan, and downwind of Lakes Erie   
   and Ontario. When it comes to >8" of snowfall, it is the eastern   
   Michigan U.P. where moderate chances (50-70%) are present.   
      
      
   ...Southern Appalachians & Mid-Atlantic...   
   Day 2...   
      
   A quick moving 500mb trough will track from the TN Valley Sunday   
   night to the Southeast Coast by Monday afternoon. 500mb PVA ahead   
   of the upper trough will be paired with easterly low-level flow   
   that allows for some upslope enhancement along the southern   
   Appalachians. Snow will be at its heaviest Monday morning but taper   
   off by Monday evening. As the upper trough sharpens on Monday over   
   the Mid-Atlantic and low pressure deepens over the Gulf Stream off   
   the Southeast coastline, some snow may also extend eastward into   
   southern VA and far northern NC. QPF and therefore snow amounts   
   have trended up with the latest guidance and should be monitored   
   over the next day or so for potentially impactful accumulating   
   snowfall. WPC probabilities currently show low- to- moderate   
   chances (30-50%) for snowfall totals >2" in portions of the VA/NC   
   Blue Ridge and Potomac Highlands of WV. Some localized totals could   
   top 4" in the VA/NC Blue Ridge.   
      
      
   ...Northern Plains & Upper Midwest...   
   Day 3...   
      
   By the second half of D3 (12z 12/9-00z 12/10) a potent shortwave   
   within the divergent left-exit region of a strong upper jet   
   extending as far westward as the central Pacific Ocean will enter   
   the northern Plains and likely produce a narrow stripe of heavy   
   snowfall. Snow will be associated with WAA on the front-end and a   
   trailing inverted trough. The thermal gradient will be tight and   
   support intense snowfall rates at times just north of the warm   
   front, but with uncertainty remaining as guidance maintains some   
   latitudinal spread and timing differences in the low track. Strong   
   winds are also likely on the backside of the system as models   
   deepen this low into the 980s, so blowing snow could be a concern   
   should these winds overlap with a snowpack. Current WPC   
   probabilities for more than 4 inches of snow through 00z Wednesday   
   are moderate (40-70%) across north-central ND through central MN.   
   However, additional snow is likely after 00z Wednesday and   
   continuing further east into WI and the Great Lakes region.   
      
      
   Mullinax/Snell   
      
      
      
      
      
   $$   
      
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