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   FOUS11 KWBC 270723   
   QPFHSD   
      
   Probabilistic Heavy Snow and Icing Discussion   
   NWS Weather Prediction Center College Park MD   
   223 AM EST Sat Dec 27 2025   
      
   Valid 12Z Sat Dec 27 2025 - 12Z Tue Dec 30 2025   
      
   *** Major Winter Storm for the Upper Midwest/Great Lakes Sunday=20   
    Night then into the Northeast Monday ***   
      
   ...The West...=20   
   Day 1... Maximum impact level from WSSI: Moderate=20   
      
   A healthy shortwave over the MT Divide this morning will continue=20   
   to move east-southeastward as a southern stream positively-tilted=20   
   trough (last gasp of the long-lived Atmospheric River event) moves=20   
   through the Great Basin into the Four Corners region. Moisture=20   
   anomalies are highest (>80th percentile) over the CO Rockies into=20   
   the Sangre de Cristos and snowfall amounts will be highest there,=20   
   generally above 9000-10,000ft.   
      
   On Saturday night the cold front associated with the strong trough   
   will quickly drop through the central High Plains and produce some   
   light/banded snow for the Denver metro region into the High=20   
   Plains. WPC probabilities for at least 8 inches of snow are highest   
   (>50%) above 8000ft or so. Lighter snow will affect the I-25=20   
   corridor from Fort Collins to Colorado Springs, but probabilities=20   
   for at least 2 inches of snow are generally less than 30%.   
      
      
   ...Southeastern New Mexico...   
   Day 3... Maximum impact level from WSSI: Minor   
      
   Cold front racing southward from the CO Rockies will leave behind=20   
   a sfc-700mb baroclinic zone along the Rio Grande as moisture from=20   
   the Pacific will still be directed eastward across northern Mexico.   
   Temperatures may be just cold enough even to the valley floors for   
   snow to accumulate, aided by an onset time overnight. WPC=20   
   probabilities for at least 2 inches of snow are >10% over most of=20   
   southeastern NM and across the TX border, and are >50% in the=20   
   Sacramento Mountains above 5000ft.=20   
      
      
   ...Great Lakes/Northeast...   
   Days 2-3... Maximum impact level from WSSI: Major   
      
   The potent northern stream trough exiting Montana will close off=20   
   as it moves across the northern Plains then digs through Iowa late=20   
   Sunday. Upper jet will become more amplified overnight and help aid   
   cyclogenesis across northern IL into Lower MI as pressures rapidly   
   drop through the 990s into the 980s mb after 00Z Monday. Snow=20   
   associated with the approaching cold front from the west will merge   
   into the developing comma-head snowfall to the northwest of the=20   
   sfc low Sunday afternoon along an inverted surface trough and on=20   
   the edge of the moisture gradient to the southeast (where PW=20   
   anomalies in the warm sector rise to >99th percentile). Snow will=20   
   expand and increase in intensity over eastern MN through=20   
   central/northern WI into the U.P. of Michigan as winds increase=20   
   from the NW to NE, picking up additional moisture from Lake=20   
   Superior. The low pressure will continue to deepen as it briefly=20   
   slows over northern Lower MI very early Monday awaiting the mid-   
   level low from the west. Shortly thereafter, it should reach peak=20   
   intensity (mid 970s mb) over Lake Huron or Georgian Bay with=20   
   continued wrap-around moisture as the WCB wraps up and around the=20   
   low. Snowfall will maximize over the northern short of the U.P.=20   
   where WPC probabilities of at least 12 inches of snow are >70%. As=20   
   the low continues through Ontario to Quebec, CAA will bring lake=20   
   effect snow to the rest of the Great Lakes into D3. WPC=20   
   probabilities for at least 6 inches of snow D3 are highest south of   
   Buffalo in the Chautauqua Ridge, aided by a multi-lake connection.   
   The bombing out of the system will induce strong winds over much=20   
   of the region, creating additional hazards due to blowing/drifting=20   
   snow.   
      
   Well ahead of the main surface low, warm air advection will=20   
   overrun cold <32F surface temperatures in the central Appalachians=20   
   into the Northeast. With precipitation starting overnight, and snow   
   on the ground through much of the region already, the WAA aloft=20   
   will have a tough time reaching the surface. This could result in a   
   widespread icing event to start for central PA northward into the=20   
   Adirondacks/eastern NY and much of New England. Without a surface=20   
   high to the north, temperatures will have an easier time rising due   
   to the freezing rain process itself, but counteracted by snow-=20   
   covered ground which could act to keep the surface warm front=20   
   farther south. It may only be when the cold front (or triple point=20   
   low) approaches that the surface inversion mixes above freezing,=20   
   albeit briefly. This may be especially true over central/northern=20   
   New England as the guidance indicates a triple point low could form   
   and act to keep northern areas below freezing at the surface. WPC=20   
   probabilities for at least 0.10" icing are >50% over parts of north   
   central PA and from the Catskills northward into the Adirondacks=20   
   and eastward through central New England (along/north of the Mass=20   
   Pike/495) and into western Maine. Greater than 50% probabilities=20   
   for at least 0.25" icing exist over the Adirondacks and into=20   
   central VT/NH. Over far northern Maine, though some icing may creep   
   that far north, snow will be the dominant ptype and WPC=20   
   probabilities for at least 4 inches of snow are >50% over the North   
   Woods.   
      
      
   Fracasso   
      
      
   ...Winter Storm Key Messages are in effect. Please see current Key   
   Messages below...   
      
   https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late=   
   stKeyMessage_1.png__;!!DZ3fjg!80PYub2ZplDosmeyJ8tIzedJLPmNrNjDbJu4BrjFSG2B9=   
   NJmNb0Hphsqi7fTPlk7IEZ7VeTsrztbptx_IacGPWZVvCQ$=20   
      
      
      
   $$   
      
   =3D =3D =3D   
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