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   FOUS11 KWBC 032015   
   QPFHSD   
      
   Probabilistic Heavy Snow and Icing Discussion   
   NWS Weather Prediction Center College Park MD   
   315 PM EST Wed Dec 3 2025   
      
   Valid 00Z Thu Dec 04 2025 - 00Z Sun Dec 07 2025   
      
      
   ...Southern/Central Rockies...=20   
   Day 1...   
      
   The sharp, positively-titled trough currently over the Four=20   
   Corners states will continue to translate eastward tonight before=20   
   ejecting into the central/southern Plains on Thursday. Forcing for=20   
   ascent downstream of this trough (in response to height falls and=20   
   modest divergence) will be enhanced by a strengthening jet streak,=20   
   especially tonight into Thursday morning. Meanwhile, Canadian high=20   
   pressure dropping into the Plains will result in impressive upslope   
   flow as cold N/NE winds develop in response. Moisture within the=20   
   region is progged to be around to slightly below normal as=20   
   reflected by NAEFS ensembles, but the impressive overlapping ascent   
   will still be favorable to support heavy snow. This will=20   
   especially be the case above 4000-5000 ft, with snow levels falling   
   in conjunction with waning snowfall intensity later tonight into=20   
   Thursday morning. The latest WPC probabilities continue to show=20   
   moderate to high chances (40-80%) for additional accumulations of=20   
   >6 inches across portions of the southern San Juans and Sangre de=20   
   Cristo mountain ranges, with low to moderate chances (20-50%) of >8   
   inches.   
      
      
   ...Great Lakes & Northeast...   
   Days 1-3...   
      
   Progressive flow across the Northeast will manifest in response to   
   a large gyre centered near Hudson Bay, which will shed periodic=20   
   shortwaves from the Great Lakes through the Northeast leading to=20   
   occasional enhanced ascent and lowered heights throughout. In=20   
   response to this evolution, multiple rounds of snowfall, sometimes=20   
   heavy, are expected through the period.=20   
      
   The first event will be associated with an arctic cold front=20   
   dragging southeast beneath a shortwave aloft. This front will move=20   
   rapidly across the eastern Great Lakes tonight, and then across the   
   Northeast on Thursday. Along and ahead of this front, the=20   
   environment continues to suggest an increasing threat for snow=20   
   squalls, especially across Upstate NY and New England on Thursday.=20   
   With 0-2km fgen maximizing along the front into elevated RH and=20   
   SBCAPE as high as 300 J/kg, widespread linear squalls are likely.=20   
   While total snowfall will be minimal in any squall, rapidly=20   
   changing conditions due to heavy snow and gusty winds will create=20   
   periods of dangerous travel Thursday afternoon and evening. As a=20   
   result, WPC has initiated Key Messages to highlight this event. See   
   the link below for more details.   
      
   Behind this front, as well as behind a subsequent shortwave on=20   
   Friday, increased CAA will spread across the Great Lakes leading to   
   periods of lake effect snow (LES). The progressive flow will=20   
   support shortwave ridging between the two impulses, so the duration   
   of any LES with each shortwave/front should be somewhat limited.=20   
   However, 850mb temps falling to between -15C to -20C Thursday, and=20   
   then between -10C to -15C late Friday into Saturday, will create=20   
   steep lapse rates and deepening inversion depths to support bands=20   
   of heavy LES. The heaviest LES snowfall accumulations within the=20   
   LES bands are expected in the typical NW snow belts across the U.P.   
   of MI, the NW L.P. near Traverse City, and then along the=20   
   Chautauqua Ridge and into the Tug Hill Plateau. In these belts,=20   
   3-day snowfall of 6-12 inches is possible, highest across the U.P.   
      
      
   ...Mid-South to the Mid-Atlantic...=20   
   Day 2...   
      
   Plenty of uncertainty heading into Day 2 with respect to a strung-   
   out shortwave exiting the Central Plains and becoming embedded=20   
   within the more zonal flow to the east. Although this shortwave is=20   
   expected to be of modest amplitude and fast moving, the=20   
   accompanying upper jet is progged to be powerful at over 150kts=20   
   across the Mid-Atlantic, leading to surface low pressure=20   
   development across the Southeast. This low will then race E/NE,=20   
   producing a swath of at least light wintry precipitation from the=20   
   Tennessee Valley to the Mid-Atlantic states.=20   
      
   There has been at least a modest northward shift/trend in the=20   
   MSLP/QPF fields from the various global ensembles the past few=20   
   runs, with the ECMWF and various machine learning suites the=20   
   farthest north. While it still remains too early to iron out the=20   
   details, WPC probabilities of 1+ inches of snow across the Central=20   
   Appalachians and into eastern VA/MD have increased to 20-60%, with=20   
   the highest chances in the higher terrain of WV/VA. WPC=20   
   probabilities for 2+ inches are between 10-20% from eastern WV to=20   
   central VA.   
      
   South of the potential moderate snow, an axis of light   
   freezing rain is also possible where a p-type transition occurs   
   underneath a stubborn layer of low-level cold air. The latest WPC=20   
   probabilities maintain a 10-30% chance for at least 0.1" of ice=20   
   across northern NC and into southern VA.   
      
      
   ...Northern to Central Rockies...=20   
   Days 1-3...   
      
   The next chance for heavy snowfall totals in the northern Rockies=20   
   will develop as a low amplitude shortwave slides off of the top of=20   
   the Pacific ridge into the region late Thursday into Friday,=20   
   coincident with the LFQ of an impressive upper jet streak swinging=20   
   across the Northern Pacific. This will result in favorable mid to=20   
   upper level forcing along with a notable influx of Pacific=20   
   moisture, sufficient for some heavy totals, especially above around   
   5000 ft as snow levels rise coincident with this moisture plume=20   
   moving into the area. Heavy snowfall accumulations are likely from=20   
   the WA Cascades through the terrain of NW WY near Yellowstone NP as   
   reflected by WPC probabilities that suggest a high risk (>70%) for   
   4+ inches, with impacts to many of the area passes becoming=20   
   likely.   
      
   Probabilities become even more impressive Day 2 and 3 across the=20   
   higher terrain from Glacier NP through Yellowstone NP including=20   
   portions of the Sawtooth/Salmon River ranges, Absarokas, terrain of   
   NW WY, northern Utah, and into the Park Range of CO. Here, WPC=20   
   probabilities Day 2 and 3 reach above 70% for 8+ inches, and Day 2=20   
   and Day 3 snowfall could be impressive above generally 6000 ft=20   
   where locally 1-2 feet is possible.   
      
   Miller/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_1.png__;!!DZ3fjg!4ONBRMdITod6KQZeFxmplUpEcL6FhhdNmsyM3cstn2js_=   
   1Nv2iBrrRRCa5z0OsCbPZ1yd7WcRTVv4VpGUAMNxmUzroo$=20   
      
      
      
   $$   
      
   =3D =3D =3D   
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