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   FOUS11 KWBC 020730   
   QPFHSD   
      
   Probabilistic Heavy Snow and Icing Discussion   
   NWS Weather Prediction Center College Park MD   
   230 AM EST Tue Dec 2 2025   
      
   Valid 12Z Tue Dec 02 2025 - 12Z Fri Dec 05 2025   
      
      
   ...Mid-Atlantic & Northeast...=20   
   Days 1...   
      
   ...Rapidly deepening coastal low will bring heavy snow to the   
   interior Mid-Atlantic and Northeast today/tonight...   
      
   Low pressure will move off the NC/VA coast this morning and then   
   track rapidly northeast along the coast, passing inside the 40N/70W   
   benchmark before lifting into the Canadian Maritimes by Wednesday   
   morning. The overlap of height falls, a coupled jet streak, and the   
   latent heat release along the offshore baroclinic gradient will   
   allow the low to rapidly deepen during this period, spreading   
   heavy precipitation and gusty winds into the Northeast.   
      
   As the low moves up the coast, persistent and impressive moist   
   isentropic ascent will surge a theta-e ridge northward to support   
   expanding heavy precipitation. The coincident WAA at 850mb will   
   produce additional ascent, with intensifying fgen driving some   
   banded precipitation, but also warm the column aloft as the surface   
   high pressure retreats rapidly to the east. The guidance has   
   trended just a bit warmer again overnight, and while most areas   
   along I-95 and points west will likely start as a brief period of   
   snow/sleet, any meaningful accumulation is anticipated only well   
   inland and at higher elevations, especially in southern and central   
   New England. The big cities from Washington, D.C. to Boston, MA may   
   start as snow before changing over to rain (and Boston may change   
   back to snow briefly before the system exits Wednesday morning).   
   However, well NW, WPC probabilities are high (>70%) for at least 6   
   inches of snow from the Catskills through the Berkshires, the   
   Worcester Hills, and across much of southern NH and ME (away from   
   the immediate coast) where locally as much as 12 inches is possible   
   (10-30% chance).   
      
   Additionally, while most of the freezing rain accompanying this   
   system is expected to wane before 12Z/Tuesday, an additional 0.1"   
   of ice is possible (10-30% chance) across the Central Appalachians   
   in the vicinity of Shenandoah NP.   
      
   Key Messages remain in effect for this system and are linked below   
   (Key Message #3)   
      
      
   ...Northern to Southern Rockies...=20   
   Days 1-2...   
      
   A shortwave digging south out of British Columbia into the=20   
   northwestern U.S. will be positioned across the interior Northwest   
   to begin the forecast period /12z Tuesday/. This shortwave will=20   
   continue to move southeast through Wednesday, and may become more=20   
   amplified as it drops through the Great Basin in response to=20   
   secondary vorticity maxima digging through its base. This will=20   
   result in a slowing and amplification of the trough, with=20   
   downstream ascent maximizing through height falls, PVA, and=20   
   downstream intensifying jet energy, especially as it approaches the   
   Four Corners Wednesday morning.   
      
   Available moisture will generally be modest as reflected by near-   
   normal PW anomalies, but the overlapped synoptic lift will be more   
   than sufficient to wring this out as periods of moderate to heavy   
   snowfall across much of the terrain. At the same time, a wave of   
   low pressure is progged to drop southeast coincident with the   
   shortwave trough, and a secondary front will also push south out of   
   Canada to cool the column while additionally leading to localized   
   upslope flow. Despite a shallow DGZ noted in regional forecast   
   soundings, the best ascent is progged to intersect within this=20   
   snow growth region to enhance snowfall, and this suggests a broad=20   
   swath of moderate snow is likely today and Wednesday across much=20   
   of the Rockies.   
      
   WPC probabilities D1 for 6+ inches are highest in the terrain above   
   5000 ft from the Salmon River/Sawtooth Range of ID through the   
   Absarokas, Little Belts, Tetons, and down into the Park Range and   
   other CO Rockies. During D2, the highest probabilities shift south   
   with the shortwave and increase, reaching above 80% for 6+ inches   
   along much of the Sangre de Cristos where locally 12+ inches is   
   likely. Additionally, as this shortwave digs south, some moderate   
   snowfall is likely along the I-25 urban corridor of Colorado,   
   bringing some notable snow to a region that has yet to experience   
   much so far this winter.   
      
   ...Great Lakes & Northeast...   
   Day 3...   
      
   A strong arctic front will race across the Great Lakes Wednesday,   
   likely reaching Upstate NY by Thursday morning before continuing   
   into New England and crossing offshore into the Atlantic Thursday   
   night. Environmental signals continue to appear favorable for snow   
   squalls along this front as it dives southeast, and the GFS and NAM   
   SnSQ parameter have both increased tonight, especially from western   
   PA through northern New England where a significant overlap of   
   0-2km fgen and SBCAPE as high as 200 J/kg exists in a region of   
   elevated low-level RH. This suggests increasing confidence in   
   linear snow squalls, especially Thursday. While snowfall=20   
   accumulations from this event will likely be minimal, brief intense   
   snow rates combined with gusty winds may create dangerous travel=20   
   across parts of the northern Great Lakes and interior Northeast.   
      
   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_3.png__;!!DZ3fjg!9CitJsY81sgfvgcKlG6ZrnnEIhWwB6pKIFXM58UDsWGWr=   
   9HKJE7T1O8YkkonalX1bNrkX6KvtEsUu9UtiQFpNXUEnak$=20   
      
      
      
   $$   
      
   =3D =3D =3D   
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