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   FOUS11 KWBC 281854   
   QPFHSD   
      
   Probabilistic Heavy Snow and Icing Discussion   
   NWS Weather Prediction Center College Park MD   
   154 PM EST Fri Nov 28 2025   
      
   Valid 00Z Sat Nov 29 2025 - 00Z Tue Dec 02 2025   
      
   ...Great Lakes & Northeast...=20   
   Day 1...   
      
   Persistent cyclonic flow will maintain the current long duration=20   
   lake effect snow (LES) event into Saturday morning leading to prolific   
   snowfall totals likely in a few areas.=20   
      
   Elongated but closed mid-level low remains centered over Quebec=20   
   driving lowered heights into the Northeastern CONUS. Rounding the=20   
   base of this trough, a secondary shortwave and elongated vorticity=20   
   lobe is swinging eastward through the western Great Lakes,   
   eventually making headway into the Northeast tonight, bringing a=20   
   brief period of shortwave ridging to the area overnight. This will=20   
   be the evolution to finally shut off the LES machine that's been=20   
   present the past 48+ hours.   
      
   However, until that transpires, two significantly impactful winter   
   weather areas continue through this afternoon and early evening.=20   
   The first is in the favored WNW snow belts off the Great Lakes:=20   
   from the eastern U.P. through the NW L.P. of MI, and then   
   downstream along the Chautauqua Ridge and the Tug Hill Plateau. 18z   
   mesoanalysis indicates a broad expanse of 850mb temps between -10   
   to -15C, driving steepening lapse rates across lake temperatures   
   that are still generally +6C to +10C according to GLERL. The   
   cooling column will keep the DGZ relatively shallow, but favorable   
   ascent crossing the DGZ efficiently has aided in producing a   
   plethora of multi-band structures with hourly rates upwards of   
   1"/hr. Hourly max rates will likely reach 2-3"/hr at times in   
   response to deep inversion depths as high as 700mb, especially in   
   the singular band structure from a long fetch axis oriented from   
   Lake Huron down through Georgian Bay then back over Lake Ontario.   
   The aforementioned persistent singular band is well-defined at this   
   hour off Lake Ontario through Oswego county extending into=20   
   southern Tug Hill and areas downstream. This area will exhibit the=20   
   heaviest snowfall accumulations through the period with areas=20   
   residing in the band likely to attain well over 12" at this=20   
   juncture leading to snowfall totals eclipsing 2ft for the entirety=20   
   of the event.   
      
   In addition to the LES, a strong cold front pressing east from the   
   Lakes has allowed for convective snow showers or snow squalls=20   
   along this front. Regional radar composite shows a multitude of   
   convectively based snow showers/squalls across southern NY state   
   down through western and central PA. The environment remains   
   favorable as the front advances east with MUCAPE as high as 200=20   
   J/kg coincident with modest 0-2km fgen and theta-e lapse rates=20   
   falling below 0C/km centered over west-central PA as of 18z. Snow   
   squall warnings have been issued in response over the past few   
   hrs, a testament to the environmental favor in place. Any area that   
   receives these snow squalls will encounter the opportunity for=20   
   dangerous travel due to rapidly changing conditions with briefly=20   
   heavy snow and gusty winds.   
      
   Key Messages remain, but will be the final issuance for the event=20   
   (link #1 below).   
      
      
   ...Northern High Plains through the Midwest into the Northeast...=20   
   Days 1-3...   
      
   ...Significant winter storm to impact large portions of the=20   
   Northern Plains, Midwest, and Great Lakes through this weekend...   
      
   The previous forecast discussion remains very relevant for the   
   incoming significant winter storm development already materializing   
   over the Plains and Midwest. Latest UA analysis this afternoon   
   indicates a positively tilted shortwave trough emerging from the=20   
   Pacific Northwest, forecast to track southeast into the=20   
   Northern/Central Plains as we continue through this afternoon. As=20   
   a secondary vorticity impulses rotates into the trough, this will=20   
   force downstream amplification of the mid-level pattern, resulting=20   
   in a negatively tilted trough and increasing ascent downstream into   
   the Midwest and Great Lakes. At the same time, jet streaks both=20   
   upstream and downstream of this amplifying trough will begin to=20   
   couple, producing even more intense deep layer lift, and a surface=20   
   low will result - first in the lee of the Rockies and then tracking   
   gradually northeast into MI by Sunday morning. This low will then=20   
   continue to deepen as it shifts across southeast Canada and exits=20   
   into the Canadian Maritimes by the end of the forecast period /12Z=20   
   Monday/.   
      
   The guidance this morning has maintained general continuity with=20   
   better agreement on the track and intensity of this system, and=20   
   while small temporal and spatial differences among the ensembles=20   
   still exist, the spread is minimal compared to previous model runs=20   
   leading to a high confidence scenario in both the expected   
   evolution and snowfall forecast. As the low deepens and moves=20   
   northeast, impressive WAA will develop downstream of the developing   
   cyclone, spreading PWs which will exceed the 90th percentile=20   
   northward into MO/IA. The accompanying theta-e ridge will surge in=20   
   tandem and isentropically ascent the region, and while guidance is=20   
   still not suggesting a strong TROWAL, at least subtle warm air=20   
   aloft will help develop modest conditional instability. The=20   
   coincident and impressive 290K isentropic ascent will lead to=20   
   expanding and intensifying precipitation, with moderate snow likely   
   across much of the Northern Plains, Upper Midwest, and Great=20   
   Lakes, especially Friday night through Sunday morning.   
      
   On D1, the heaviest snowfall accumulations are likely in a narrow   
   band driven by the jet streak aloft and the accompanying   
   ageostrophic/fgen enhancement between 700-600mb. This has allowed   
   for a stripe of periodically heavy snow over parts of the Dakotas,   
   spreading into western IA as of the past few hrs. Despite the band=20   
   being relatively narrow, snowfall rates of 0.5"-1"/hr are likely=20   
   which could cause 4-6" of snow as reflected by WPC probabilities=20   
   for 4+ inches that reach above 70%.   
      
   However, the most significant part of this event begins later this   
   evening across IA, spreading eastward through D2 IL/WI/MI. Here,=20   
   the impressive isentropic ascent will be quite moist as reflected=20   
   by mixing ratios of 4 g/kg on the 290K surface, leading to a=20   
   rapidly saturating column. While in general this upglide will=20   
   result in moderate snowfall rates, there appears to be an=20   
   increasing risk for heavier snowfall across portions of MO/IA/IL as   
   the WAA forces an increasing isothermal layer beneath the DGZ=20   
   which also begins to deepen. Cross-sections are more robust=20   
   featuring a corridor of folding theta-e surfaces within the=20   
   elevated RH, suggesting a greater potential for CSI and convective=20   
   snowfall rates. There is still some uncertainty into this since=20   
   this signal is much more robust tonight than previous model runs,=20   
   but locally 1-2"/hr rates appear possible which is supported by the   
   WPC prototype snowband tool despite a modest overall appearance of   
   the evolution with respect to conceptual models for heavy snow=20   
   bands. Still, multiple bands lifting northward for a long duration=20   
   will result in significant snowfall accumulations and major impacts   
   for the post- Thanksgiving holiday travel.=20   
      
   This will be a significant system with several waves of moderate to   
   heavy snowfall. On D2, the heaviest accumulations are expected from   
   far eastern NE through IA, northern IL, and southern WI. WPC   
   probabilities in this region are 70-100% for more than 6 inches of   
   snow, and locally as high as 50-70% for more than 12 inches,=20   
   highest near the Cedar Rapids over into the Quad Cities of IA.=20   
   Later D2 into D3 the heaviest snow shifts eastward and eventually=20   
   wanes in intensity, but additional heavy snowfall exceeding 6" is=20   
   possible, especially around Lake Michigan and into the L.P. of MI.=20   
   Event total snowfall may reach upwards of 15+" in isolated=20   
   locations Saturday, potentially setting November and even=20   
   encroaching some all-time snowfall records for the 24hr and 48hr=20   
   periods.   
      
   Moderate snowfall is also expected across the interior northeast=20   
   where WPC probabilities D3 are as high as 50-70% for 4+ inches in=20   
   the higher terrain of VT, NH, and ME.   
      
   Key Messages remain in effect for this system (Link #2 below).   
      
      
   ...Central Rockies...   
   Day 3...   
      
   No changes necessary to the anticipated evolution of the next   
   winter disturbance to impact the Central Rockies. A potent=20   
   shortwave will drop out of the Pacific Northwest Sunday morning,   
   moving progressively southeast, reaching the Four Corners Sunday=20   
   night while maintaining a positive tilt. Late D3 this feature will=20   
   begin to sharpen, with the resulting downstream jet streak=20   
   intensifying into the Central Plains. The overlap of the RRQ of=20   
   this jet streak with the greatest height falls ahead of the trough=20   
   axis will help spawn low pressure in the Great Basin, and this low=20   
   will help to increase ascent across the Central Rockies Sunday=20   
   evening. As the overall ascent increases, precipitation will=20   
   expand, and periods of moderate to heavy snow are likely, generally   
   above 5000 ft. This system is expected to remain progressive so=20   
   prolonged snowfall is not expected, but WPC probabilities indicate=20   
   a moderate risk (50-80% chance) of at least 6 inches of snowfall=20   
   across the CO Rockies and northern San Juans, with lighter=20   
   accumulations expected as far west as the Wasatch of Utah.   
      
      
   Weiss/Kleebauer   
      
      
   ...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!9HzmYz-mIE6DfhJQQBQsOzECv_KFcaoJzdylhJVfCiVsb=   
   -Dbu3RKVB1zEOHkADoLaYbeS0vS7lK--9jlNEGcykLqUmg$=20   
      
   https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late=   
   stKeyMessage_2.png__;!!DZ3fjg!9HzmYz-mIE6DfhJQQBQsOzECv_KFcaoJzdylhJVfCiVsb=   
   -Dbu3RKVB1zEOHkADoLaYbeS0vS7lK--9jlNEGckf1n8zY$=20   
      
      
      
   $$   
      
   =3D =3D =3D   
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