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   FOUS11 KWBC 172100   
   QPFHSD   
      
   Probabilistic Heavy Snow and Icing Discussion   
   NWS Weather Prediction Center College Park MD   
   400 PM EST Wed Dec 17 2025   
      
   Valid 12Z Wed Dec 17 2025 - 12Z Sat Dec 20 2025   
      
      
   ...Cascades and Northern Rockies...=20   
   Days 1-3...   
      
   An anchored -WPO/-PNA teleconnection pattern is the driver in the   
   seemingly endless barrage of atmospheric rivers that is delivering   
   copious amounts of snow to the mountains of the Pacific Northwest   
   and the Northern Rockies. As a colder air-mass becomes entrenched=20   
   across the Columbia Basin and Northern Rockies. Snow levels are   
   between 2,500-3,000ft in the Cascades and as low as 2,000ft in the   
   Lewis Range at the onset as moderate precip rates persisting=20   
   behind this cold front today generate impactful snow below pass=20   
   level. Snow levels in the core of this AR will rise to over 9000ft=20   
   in OR Thursday morning and 5000 to 6000ft in WA by Thursday   
   afternoon with a powerful cold front shifting south over WA=20   
   Thursday night. Farther east, snow levels will rise to 6,000t in=20   
   the Bitterroots by Thursday night and approach 7,000ft in the   
   Sawtooth. Before the snow levels rise, however, strong 700mb FGEN   
   will support several hours of heavy snow at elevations as low as   
   6,000ft in central ID and 5,000ft in the Blue Mountains through=20   
   Thursday afternoon. Farther south, the Tetons, Absaroka, and Wind   
   River Ranges will reside closer to stronger 700mb jet and=20   
   anomalous PWATs, giving these ranges both an abundance of moisture=20   
   and strong upslope enhancement to keep heavy snow in the forecast=20   
   through Saturday morning for elevation at and above 7,000ft.=20   
      
   Prolonged Pacific moisture flux continues to be directed at OR and   
   into the Northern Rockies on Friday with higher snow levels that   
   support heavy snow in the more remote reaches of the Cascades and   
   Northern Rockies. The lone exception will be ongoing westerly upslope   
   flow into the WA Cascades where snow levels as low as 1,500ft are   
   expected. The bulk of the heaviest snowfall in the WA Cascades and   
   Olympics above 2,500ft. WPC 72-hour probabilities show high chances   
   probabilities (>70%) for snowfall totals >24" at elevations between   
   3,000-4,000ft, while similar high chance probabilities exist above   
   4,000ft for snowfall totals >30". In the Rockies, high chance   
   probabilities (>70%) for >12" of snow are present above 5,000ft in   
   the Blue Mountains, Bitterroots, and the Lewis Range, while those=20   
   same probabilities for >24" are present above 6,000ft in the   
   Sawtooth. Snowfall in the Tetons and Wind River Ranges are likely   
   to range between 1-3 feet with some localized amounts approaching=20   
   4 feet in the more remote reaches of these ranges through=20   
   Saturday.   
      
   ...Northern Plains, Upper Midwest, Great Lakes...=20   
   Days 1-3...   
      
   A potent shortwave trough, currently located over the Northern   
   Rockies, is forecast to amplify and close off in response to a 180   
   kt Eastern Pacific jet digging southward into the Four Corners=20   
   today. At the surface, a strong sub-980 mb low pressure center=20   
   will track southeastward into the Northern Plains, before an=20   
   emergent triple- point low migrates across the Upper Midwest=20   
   tomorrow and Friday.=20   
      
   As this low ejects eastward tonight, strengthening theta-e   
   advection from the Gulf combined with moist eastern Pacific inflow   
   will result in precipitable water anomalies in the 99th percentile   
   upstream of a developing TROWAL on the northwest flank of the low=20   
   center. With the entrance region of a strengthening jet streak=20   
   situated over the Canadian prairie, a heavy snow band is expected=20   
   to develop in the comma-head region roughly from a Glasgow to=20   
   Bemidji line. The progressive nature of this system will cap=20   
   overall heavy snow potential, but intense ascent superimposed with=20   
   a deep DGZ will yield at least a brief window for heavy snowfall=20   
   tonight and tomorrow morning. The latest WPC probabilities for >6"=20   
   of snow have dipped somewhat compared to the latest cycle, but=20   
   still highlight a 40-50% chance through Day 1 immediately along the   
   International Border, while 70-90% probabilities for >2" of=20   
   snowfall are noted in adjacent areas. Although the total snowfall=20   
   from this event may look modest for this region, strong wind gusts=20   
   upwards of 70 mph will lead to dangerous travel due to blowing snow   
   and potential blizzard impacts. Along the same lines, snow squalls   
   remain possible along the leading edge of a surging Arctic front=20   
   across eastern Montana, the Dakotas, and Minnesota through=20   
   tomorrow.=20   
      
   The probability of significant icing is less than 10 percent.=20   
      
      
   Mullinax/Asherman/Jackson   
      
      
      
      
   ...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!4RZVcz-ODCFsrekcV_tv1tRZsR5od7QH8Qcqffv7d5tsg=   
   yOJC5zCU-vAU2n-70KlUZF_YjQ95dWWP79tX5RKZgUhHJ8$=20   
      
      
      
   $$   
      
   =3D =3D =3D   
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