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   FOUS11 KWBC 272054   
   QPFHSD   
      
   Probabilistic Heavy Snow and Icing Discussion   
   NWS Weather Prediction Center College Park MD   
   354 PM EST Sat Dec 27 2025   
      
   Valid 00Z Sun Dec 28 2025 - 00Z Wed Dec 31 2025   
      
   *** Major Winter Storm for the Upper Midwest/Great Lakes Sunday=20   
    Night then into the Northeast Monday ***   
      
   ...Southern Rockies onto the High Plains...=20   
   Day 1... Maximum impact level from WSSI: Moderate   
      
   Northern stream shortwave trough axis over central MT will close   
   into a low over ND tonight as a reinforcing shortwave dives   
   southeast over WY. Remnant Pacific moisture will continue to   
   maintain moderate snow rates over the CO and northern NM Rockies   
   tonight with snow levels decreasing to valley floors before snow   
   tapers off early Sunday. Day 1 PWPF for >6" additional after 00Z=20   
   are 50-70% for northern and western CO Rockies.   
      
      
   The cold front associated with the strong trough will quickly drop   
   through the central High Plains tonight where left exit dynamics   
   from a SWly jet ahead of the trough will aid snow and development=20   
   for the Denver metro region east into Nebraska late tonight into   
   Sunday. Day 1 PWPF for >2" are 30-50% for the Palmer Divide and   
   generally less than 10% for the High Plains, though this phenomena   
   is rarely picked up well by models.=20   
      
      
   ...Southeast New Mexico/Guadalupe Mountains...=20   
   Days 2/3... Maximum impact level from WSSI: Moderate   
      
   Cold front racing southward from the CO Rockies Sunday will leave=20   
   behind a sfc-700mb baroclinic zone along the Rio Grande as moisture   
   from the Pacific will still be directed eastward across northern=20   
   Mexico. Temperatures may be just cold enough even to the valley=20   
   floors for snow to accumulate, aided by an onset time early Monday   
   with the threat continuing through Monday night. Topographic   
   enhancement on the Guadalupe and southern Sacramento Mtns raises   
   Day 2 PQPF for >4" into the 20-40% range in this terrain.   
      
      
   ...Great Lakes/Northeast...   
   Days 2-3... Maximum impact level from WSSI: Major   
      
   The potent northern stream trough exiting Montana this evening=20   
   will close off over ND tonight and jog southeast to Iowa Sunday as   
   southern stream elements phase in. This will promote rapid surface=20   
   cyclogenesis as it tracks from northern IL Sunday afternoon through   
   Lower MI Sunday night.=20   
      
   Snow associated with the approaching cold front from the west will   
   merge into the developing comma-head snowfall to the northwest of=20   
   the sfc low over MN/northern WI Sunday afternoon along an inverted   
   surface trough and on the edge of the moisture gradient to the=20   
   southeast (where PW anomalies in the warm sector rise to >99th=20   
   percentile). Snow will expand and increase in intensity over=20   
   northern WI/U.P. of MI Sunday evening, quickly becoming enhanced by   
   Lake Superior as cyclonic flow rapidly intensifies. Meanwhile,   
   east/ahead of the low center will be a wintry mix over the northern   
   L.P. and eastern U.P. with sleet and freezing rain eventually   
   giving over to snow early Monday.   
      
   The low pressure will continue to deepen as it briefly slows over=20   
   Lake Huron early Monday as the system becomes vertically stacked=20   
   and occludes. awaiting the mid- level low from the west. Peak   
   intensity is then Monday morning with MSLP in the mid 970s over=20   
   Lake Huron or Georgian Bay with the warm conveyor belt now   
   completed wrapped up and around the low. Snowfall will maximize=20   
   over the northern shore of the U.P. where powerful onshore flow=20   
   pivots as the low passes with 1-2ft likely. Day 1.5 PWPF for >6"=20   
   are over 20% from northern Iowa across eastern MN and central WI,=20   
   expanding across the northern and western L.P. for Day 2.   
      
   Strong westerlies then scream east Monday promoting turbulent LES   
   banding off Lake Michigan with single banding threats off Lakes=20   
   Erie and Ontario coupled with blowing/drifting snow. Day 3 PWPF=20   
   for >8" are over 50% above Erie, PA through the Chautauqua Ridge=20   
   and south towns of Buffalo as well as across Syracuse and up=20   
   through the Tug Hill Plateau.=20   
      
   Well ahead of the main surface low, warm air advection will=20   
   overrun cold <32F surface temperatures from central PA Sunday   
   afternoon through the Northeast Sunday night. Given snow is on the   
   ground through much of the region, the WAA aloft will have a tough   
   time reaching the surface. Day 1.5 PWPF for >0.1" is 40-60% in   
   central PA across the Catskills and southern New England with Day 2   
   PWPF for >0.25" 50-70% for the northern Hudson Valley through the   
   Adirondacks and along the St Lawrence, and across VT/NH into   
   Maine. It is worth noting that without a surface high to the=20   
   north, temperatures will have an easier time rising due to the=20   
   freezing rain process itself, but again 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.=20   
   A snow line looks to set up over far northern NH and northwestern   
   Maine where Day 3 PWPF for >4" are 40-60%.   
      
      
   Jackson   
      
      
      
   ...Winter Storm Key Messages are in effect for the Great Lakes and   
   Northeast and linked below...   
      
   https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late=   
   stKeyMessage_1.png__;!!DZ3fjg!-DKELbdACovotXfhPRFe2xuGWS9RPcu6ogCKXoshfphFi=   
   ETLGYltZgapEL0F8gRS-iECCckrboM33Ho2Tm9UNagCyeI$=20   
      
      
      
   $$   
      
   =3D =3D =3D   
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