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   FOUS11 KWBC 182052   
   QPFHSD   
      
   Probabilistic Heavy Snow and Icing Discussion   
   NWS Weather Prediction Center College Park MD   
   352 PM EST Thu Dec 18 2025   
      
   Valid 00Z Fri Dec 19 2025 - 00Z Mon Dec 22 2025   
      
      
   ...Blizzard conditions continue in the Northern Plains through this   
   evening. See Key Messages linked at the bottom of the discussion=20   
   for more information...   
      
   ...Northern Plains, Upper Midwest, Great Lakes...=20   
   Days 1-2...   
      
   At the beginning of the forecast period (00z Fri.) a strong 984 mb   
   cyclone is forecast to jog northeastward across Lake Superior into   
   Ontario. While snowfall is rapidly subsiding across the Northern=20   
   Plains, blizzard conditions will persist into early this evening=20   
   across portions of the eastern Dakotas and western Minnesota owing   
   to the gradient winds and fresh snowpack. 1-2" of blowing snow is   
   also expected over portions of the Minnesota Arrowhead and Upper=20   
   Peninsula of Michigan, which will support periods of hazardous=20   
   travel through early tomorrow.=20   
      
   As this system continues eastward tonight into Friday, gusty winds   
   and developing lake effect snow are the most likely winter-related=20   
   hazards. 850 mb temperatures as low as -15C to -20C are expected   
   behind the strong cold front as lake temperatures remain largely   
   around 5C. This temperature delta and brief surge of west-   
   northwesterly flow will allow for heavy lake effect snow in the   
   typical snowbelts downwind of Lake Superior and Michigan, with   
   additional heavy snow possible downwind of Lake Erie and Lake   
   Ontario. The highest WPC probabilities for at least 6" of snow   
   through Saturday morning is across the Tug Hill Plateau downwind of   
   Lake Ontario, where chances sit at 40-70%.=20   
      
   ...Cascades, Northern Rockies, & Northern California...=20   
   Days 1-3...   
      
   An anchored -WPO/-PNA teleconnection pattern is the culprit in the=20   
   endless barrage of atmospheric rivers generating copious amounts=20   
   of snow throughout the mountains of the Pacific Northwest and the=20   
   Northern Rockies. A persistent feed of Pacific moisture continues=20   
   to stream as far east as the northern Rockies today. Snow levels=20   
   in the core of this AR will rise to over 9000ft in Oregon and=20   
   6000-7000ft in eastern WA. By this evening, a potent cold front=20   
   advancing south over western WA tonight leads to snow levels   
   crashing below 2000ft. Farther east, snow levels will rise to=20   
   6000t in the Bitterroots by tonight and approach 7000ft in the=20   
   Sawtooth. Before the snow levels rise, however, strong 700mb FGEN=20   
   is supporting several hours of heavy snow at elevations as low as=20   
   6000ft in central ID and 5000ft in the Blue Mountains through this=20   
   evening. Farther south, the Tetons, Absaroka, and Wind River Ranges   
   will reside closer to stronger 700mb jet and anomalous PWATs (>99th   
   ECMWF climatological percentiles through Friday afternoon), giving   
   these ranges both an abundance of moisture and strong upslope=20   
   enhancement to keep heavy snow in the forecast through Saturday=20   
   morning for elevation at and above 7000ft.=20   
      
   Prolonged Pacific moisture flux will drift southward on Friday with   
   precipitation spreading across northern CA and continue through   
   Sunday. Snow levels dip to as low as 5,000ft in the Siskiyou and   
   Shasta, but they only fall in the 8,000-9,000ft elevations on   
   Saturday before increasing above 9,000ft on Sunday. The lone=20   
   exception to the higher snow levels and SLRs will be ongoing=20   
   westerly upslope flow into the WA Cascades where snow levels as low   
   as around 1,500ft on Saturday and 2,500 ft on Sunday. The bulk of=20   
   the heaviest snowfall in the WA Cascades and Olympics is expected=20   
   above 2500ft. WPC 72-hour probabilities show high chances=20   
   probabilities (>70%) for snowfall totals >18" between 3,000-   
   4000ft, while similar high chance probabilities exist above 4,000ft   
   for snowfall totals >30". In the Rockies, high chance=20   
   probabilities (>70%) for >12" of snow through Friday are present=20   
   above 5,000ft in the Blue Mountains, Bitterroots, and the Lewis=20   
   Range, while those same probabilities for >18" are present above=20   
   6,000ft in the Sawtooth. Snowfall in the Tetons and Wind River=20   
   Ranges are likely to range between 1-3 feet with some localized=20   
   amounts approaching 4 feet in the more remote reaches of these=20   
   ranges through Sunday. The WSSI is keying in on Extreme Impact   
   potential (extremely dangerous travel, damages to infrastructure=20   
   in the Wind River, Teton, and Absaroka ranges through Friday night,   
   largely in the higher reaches of these ranges. Still, Major=20   
   Impacts (significant travel disruptions) at intermediate=20   
   elevations of these ranges are likely with heavy snow and whiteout   
   conditions contributing to the impacts in these ranges to close=20   
   out the week.=20   
      
      
   The probability of significant icing is less than 10 percent.=20   
      
      
   Mullinax/AA/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!5l8mDKSbTrGBB2HZ5yAGCRsE22fZKp_zFc6mg68TKkrT-=   
   yNKKjx6qWc5iTxkj-ZSZYprAhzHoh0jGvl5g8UgyrjDGZo$=20   
      
      
      
   $$   
      
   =3D =3D =3D   
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