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   FOUS11 KWBC 010804   
   QPFHSD   
      
   Probabilistic Heavy Snow and Icing Discussion   
   NWS Weather Prediction Center College Park MD   
   304 AM EST Mon Dec 1 2025   
      
   Valid 12Z Mon Dec 01 2025 - 12Z Thu Dec 04 2025   
      
      
   ...Central Plains through the Mid-Atlantic & Northeast...=20   
   Days 1-3...   
      
   ...Widespread moderate to heavy snow from the Central Plains to the   
   Northeast will impact travel early this week while treacherous   
   icing occurs across the Appalachians...   
      
   A potent but positively tilted mid-level shortwave trough will be   
   advancing eastward from the Four Corners to start the period /12Z   
   today/ and move progressively eastward into the Ohio Valley by   
   Tuesday morning. During this translation, the feature, while   
   remaining of modest amplitude, may take on at least a neutral tilt   
   as vorticity continues to swing through the base of the   
   accompanying parent trough, and the entire system should be off the   
   New England Coast by 12Z Wednesday with only subtle amplification   
   expected. Although this shortwave will remain modest overall, the   
   accompanying jet streaks, both a downstream intensifying feature   
   and the broader subtropical jet lifting out of Mexico, are expected   
   to phase across the southern/central Plains today. The increasing   
   ascent left by the resulting RRQ overlapping height falls from the   
   shortwave will result in surface cyclogenesis along the Gulf Coast   
   tonight. This surface low is then expected to track rapidly   
   northeast across the southern Mid-Atlantic states and then deepen   
   just inside the 40N/70W Benchmark Tuesday night before lifting into   
   into the Canadian Maritimes.   
      
   This evolution will result in widespread snow and freezing rain   
   across the eastern half of the country, with two distinct areas of   
   impactful wintry precipitation.   
      
   On the north side of this system, a swath of moderate snow is   
   expected on D1 from Kansas through the Ohio Valley. This is in   
   response to the strengthening/phased jet streak which will begin to   
   tilt poleward to support impressive upper diffluence. At the same   
   time, some mid-level frontogenesis will be intensified by this jet   
   streak, forcing favorable overlap of ascent into the deepening DGZ   
   (SREF probabilities for 100mb of depth over 30% now) which will   
   support heavy snowfall rates within a translating band of 1"/hr or   
   more at times, aided by fluffy SLRs. The guidance has trended=20   
   upward with this feature, and WPC probabilities indicate a 10-30%   
   chance for at least 4 inches of snow from near Kansas City through   
   just south of Chicago.   
      
      
   As this band moves east into the Ohio Valley, it will become=20   
   merged with the larger system developing near the Gulf as=20   
   impressive moist isentropic ascent begins and lifts a theta-e ridge   
   northward to expand the precipitation shield. The strong 850mb WAA   
   will provide additional ascent, with the accompanying fgen serving   
   to intensify omega into the DGZ. While the WAA will likely result=20   
   in a burst of moderate snowfall in many areas from the Mid-   
   Atlantic/Ohio Valley northeast, a lack of resupplying cold air as=20   
   the surface high retreats will enable a quick transition to=20   
   mixed/rain, especially along and east of I-95 between VA and MA.=20   
   However, NW of the I-95 corridor, a prolonged period of moderate to   
   at times heavy snow is likely, with 1+"/hr rates spreading from PA   
   to ME. This will create an axis of snowfall for which WPC=20   
   probabilities indicate a high risk (>70% chance) for 4+ inches from   
   the Poconos through Downeast Maine, with locally as much as 8-12=20   
   inches possible (50% chance) from the Berkshires through the=20   
   Monadnock region of NH and into southern ME.   
      
   It is important to add as well, that despite what should be a   
   relatively quick transition from snow to mix to rain along I-95,   
   the Tuesday morning commute could be significantly impacted.   
      
   South of the heavy snow axes, two areas of impactful freezing rain   
   are also anticipated. The first will be across portions of   
   AR/MO/KY, in the vicinity of the Ozarks on Monday morning as   
   isentropic ascent and the accompanying moisture plume spread   
   precipitation into this region. Initially, surface wet-bulb   
   temperatures will be sub-freezing, so precipitation will fall as   
   freezing rain in response to the warm nose pivoting overhead.   
   However, this p-type should generally be short lived except in the   
   coldest regions, and WPC probabilities for 0.1" of ice peak around   
   30% in central AR.   
      
   More significant icing is likely across portions of the central and   
   southern Appalachians as isentropic ascent and accompanying WAA   
   intensify Monday night into Tuesday. Here, wet-bulb temperatures   
   will again be below freezing leading to an extended period of   
   freezing rain from SW NC into western MD. Although the high   
   retreats, this cold air may be more challenging to scour out,   
   especially in the higher elevations, leading to an extended period   
   of freezing rain with impactful ice accretions likely. WPC   
   probabilities D1 into D2 suggest a high risk (>70%) for at least   
   0.1" of icing from western NC through the Shenandoah region of VA,   
   with a low chance (10-30%) of up to 0.25" in isolated locations.   
      
   Key Messages remain in effect for this system and are linked below   
   (Key Message #3)   
      
      
   ...Northern to Southern Rockies...=20   
   Days 2-3...   
      
   A shortwave digging out of British Columbia embedded within broad   
   cyclonic flow across the eastern half of the CONUS will spread   
   increasing synoptic ascent across the Intermountain West beginning   
   Tuesday morning. This shortwave will move progressively southeast   
   Tuesday, and may become more amplified despite maintaining a strong   
   positive tilt by Wednesday morning in response to secondary   
   vorticity maxima digging through its base. This will result in a   
   slowing and amplification of the trough, with downstream ascent   
   maximizing through height falls, PVA, and downstream intensifying   
   jet energy.=20   
      
   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 may maximize within this snow growth   
   region to enhance snowfall, and this suggests a broad swath of   
   moderate snow is likely Tuesday and Wednesday across much of the   
   Rockies.   
      
   WPC probabilities for 4+ inches D2 are highest from MT through WY,   
   with local maxima in snowfall above 8 inches possible across the   
   Little Belts and Absarokas, with snow levels running around   
   2000-3000 ft. By D3, the heaviest snow pivots southeast reaching   
   the CO Rockies, the San Juans, and Sangre de Cristos, where WPC   
   probabilities indicate a moderate risk (50-70%) for 6+ inches of   
   snowfall. Snow levels continue to fall on Wednesday as well such   
   that even the I-25 urban corridor from Cheyenne to Santa Fe may   
   experience a few inches of snow, with the higher accumulations   
   expected across the Raton Mesa and Palmer Divide.   
      
      
   ...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 beyond this forecast period. While confidence is   
   low at this time, the signals appear favorable for snow squalls   
   along this front as it dives southeast. The trends in the GFS SnSq   
   parameter have decayed a bit in recent runs, but the environment at   
   this time frame appears at least marginally favorable for a line,   
   or lines, of convective snow showers/snow squalls Wednesday into   
   Thursday. While snowfall amounts will be minimal, snow squalls can   
   cause dangerous driving due to briefly heavy snow rates and gusty   
   winds, so this event will need to be monitored as it gets closer.   
      
      
   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!5yQB3jpQNoHGi7CLwb89D4XfQqfQD6y2WYs0GA0deyuOX=   
   5XM7r-Hwq9HUl0fa45gZku1edttTkTaRH-BsCW62nKKERs$=20   
      
      
      
   $$   
      
   =3D =3D =3D   
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