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   FOUS11 KWBC 010834   
   QPFHSD   
      
   Probabilistic Heavy Snow and Icing Discussion   
   NWS Weather Prediction Center College Park MD   
   334 AM EST Thu Jan 1 2026   
      
   Valid 12Z Thu Jan 01 2026 - 12Z Sun Jan 04 2026   
      
   ...Eastern Maine...=20   
   Day 1...   
      
   Potent upper trough will swing across New England today, with an   
   embedded vorticity maxima lifting into the Canadian Maritimes   
   Thursday night. The evolution of this vorticity max combined with   
   at least the distant LFQ of a southeast diving upper jet will allow   
   a surface low to deepen as it tracks across Northern New England,   
   intensifying more rapidly in response to a negative tilt of the   
   upper trough this evening into Canada. While in general this=20   
   system will be progressive, an inverted trough positioned west of=20   
   the primary low will rotate across eastern Maine as the low shifts=20   
   northward, leading to a longer duration of moderate to heavy=20   
   snowfall rates (30-50% chance of 1"/hr). This will result in a=20   
   swath of moderate snowfall accumulations for which the WPC   
   probabilities indicate has a moderate chance (50-70%) of exceeding   
   6 inches, highest across Downeast Maine.   
      
      
   ...Great Lakes...   
   Days 1-3...   
      
   An arctic front passing east of the Great Lakes early this morning   
   will leave impressive CAA in its wake, while cyclonic flow asserts   
   itself across the region. This cyclonic flow will be secondary   
   enhanced late Thursday night into Friday as another shortwave   
   passes through the flow, leading to renewed CAA before shortwave   
   ridging develops by the end of the forecast period.   
      
   While this arctic front will maintain a snow-squall risk through   
   early this morning into New England and the Mid-Atlantic (for which   
   Key Messages remain in effect, linked at the bottom of this   
   discussion) the primary hazard becomes widespread heavy lake effect   
   snow (LES) in the favored W/NW snow belts. The most intense LES   
   will likely begin late tonight as 850mb temperatures plummet to as   
   low as -15C to -20C, across lakes that, while they have cooled,=20   
   are mostly ice-free. This will lead to impressive SBCAPE as high   
   5000-1000 J/kg to support a long duration 1-2+"/hr LES event,   
   especially downwind of Lakes Erie and Ontario due to upstream   
   connections. The heaviest accumulations D1 and D2 are expected   
   across the Chautauqua Ridge and along//just barely south of the=20   
   Tug Hill plateau before shifting a little south into D2. WPC   
   probabilities are high (>90%) for 6+ inches in these areas D1,   
   continuing east of Lake Ontario D2. Locally 2-4 feet of snow is   
   possible east of Lake Ontario before LES wanes during D3. Downwind   
   of the other Great Lakes, WPC probabilities D1 feature a moderate   
   risk (50-70%) for 6+ inches in the eastern U.P., but this wanes   
   quickly during D2.   
      
      
   ...California through the Central Rockies...=20   
   Days 1-3...   
      
   A deep trough in the subtropical Eastern Pacific will lift=20   
   NNE through the central CA coast early today before crossing the=20   
   Sierra Nevada and into the Great Basin by Friday morning. The   
   primary shortwave within this trough will crest an expanding ridge   
   (amplifying downstream of a more intense trough over the Pacific)   
   and drop into CO and the High Plains Friday morning/aftn.,=20   
   As the trough moves inland, snow levels on the Sierra Nevada will=20   
   fall to around 7500ft this afternoon, bringing heavy snow until=20   
   precipitation ends this evening. Farther east, and continuing   
   downstream of this trough/impulse, snow levels will remain elevated   
   at 7000-8000 ft, but precipitation falling as snow will spread   
   across much of the Great Basin and Four Corners at the higher   
   elevations. WPC probabilities D1 for 6+ inches of snow reach above   
   70% in the Sierra, and locally as high as 70% in portions of the   
   Wasatch and CO Rockies. Precipitation will linger through D2 across   
   the Four Corners terrain, but with generally a waning trend.   
      
   Then on D3 a more pronounced surge of precipitation spreads onshore   
   CA once again as a deep trough amplifies offshore, resulting in   
   impressively amplified southerly flow. This will push moisture   
   onshore as IVT exceeds 500 kg/m/s (>80% chance). Once again snow   
   levels will be elevated within the accompanying WAA, reaching as   
   high as 8000 ft into the Sierra (although much lower around 6000 ft   
   across the Shasta/Trinity region). The pronounced moisture will   
   result in heavy snow again above these levels, and with SLR   
   expected to be low, it will be an impactful snowfall due to snow   
   load. WPC probabilities D3 are high (>90%) for more than 6 inches   
   across these mountains, with locally more than 12 inches possible   
   (30-50% chance) in the Sierra.   
      
      
   ...Columbia Basin and Gorge...   
   Day 1...   
      
   Increasing southerly mid-level flow over the Pacific Coast will   
   spread moisture northward, aided by a weakening shortwave lifting   
   from CA into the northern Great Basin. As this moisture spreads   
   into the Pacific Northwest, it will overrun a slowly retreating   
   ridge of high pressure, manifesting with easterly winds draining   
   into the Columbia Basin/Gorge to maintain cold surface air. This   
   setup is favorable for light freezing rain with modest accretions   
   as reflected by WPC probabilities that reach as high as 70% for 0.1   
   inches of ice. Although amounts are generally light, impacted=20   
   travel is likely tonight into Friday morning due to slippery=20   
   roadways.   
      
      
   Weiss   
      
      
   ...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!4KcpeRfEaE90L2aFopU7nqHmEr2kAB4kKifoH1AxvdJX1=   
   x1YD-GsTigUG8uJqvwrOLksvrurJKgrhdg4n79dPyZCvaE$=20   
      
      
      
   $$   
      
   =3D =3D =3D   
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