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   FOUS11 KWBC 040755   
   QPFHSD   
      
   Probabilistic Heavy Snow and Icing Discussion   
   NWS Weather Prediction Center College Park MD   
   255 AM EST Thu Dec 4 2025   
      
   Valid 12Z Thu Dec 04 2025 - 12Z Sun Dec 07 2025   
      
      
   ...Great Lakes & Northeast...   
   Days 1-3...   
      
   A progressive and flow pattern over the Great Lakes will result in   
   periodic episodes of snow squalls and LES bands as a -AO/NAO regime   
   cuts off a large upper low over southeast Canada and builds a ridge   
   over Greenland and the Davis Strait. Today, an Arctic front=20   
   traversing the Great Lakes will act as a trigger at low-levels at   
   the same as the divergent left-exit region of a 250mb jet streak   
   places itself over the Northeast. Latest NAM shows 0-2km FGEN along   
   the front that is paired with a well-saturated low-level profile   
   and SBCAPE as high as 300 J/kg. As the front traverses the region,   
   the DGZ will grow within the 900-800mb layer and squalls will be   
   capable of producing bursts of heavy snow and gusty winds. While   
   snow accumulations will likely be limited in most cases due to the   
   squalls' progressive movement, surface and road temperatures=20   
   around freezing will drop into the 20s in wake of the front,=20   
   allowing for untreated surfaces to become icy and hazardous.=20   
   Whether it be by snow accumulating on all surfaces, melting and=20   
   refreezing on untreated surfaces, or the rapid reductions in=20   
   visibility, snow squalls have the potential to produce dangerous=20   
   driving conditions in the matter of seconds. WPC continues to issue   
   Key Messages for the snow squall threat for today (see Key=20   
   Messages link below).   
      
   In wake of the Arctic frontal passage, a pair of sheared shortwave   
   troughs within a broad cyclonic flow pattern will direct a pair of   
   frontal systems across the Great Lakes. Rounds of light-to-moderate   
   snowfall will ensue over the Upper Great Lakes Thursday night and   
   into Friday, with another cold kicking up additional LES bands in   
   the typical LES belts of the region. WPC probabilities show low-   
   to-moderate chances (30-50%) for snowfall totals >4" through Friday   
   and Saturday in Michigan's U.P., the western LES band belts of   
   Michigan's Mitten, and downwind of Lakes Erie and Ontario.   
      
      
   ...Mid-South to the Mid-Atlantic...=20   
   Days 1-2...   
      
   Guidance is coming into better agreement on a winter setup that   
   is likely to produce some of the first winter hazards of the season   
   from the Mid-South to the Mid-Atlantic beginning today and lasting   
   through Friday. A shortwave trough over the south-central Plains=20   
   today will weaken as it makes its way east. Despite this 500mb=20   
   trough losing its punch, a strong ridge of high pressure over the=20   
   Bahamas and a large upper-low over Hudson Bay has led to the=20   
   formation of a robust 250mb jet streak oriented SW-NE over the=20   
   east-central U.S.. Beneath the diffluent right-entrance region, a=20   
   weak wave of low-pressure along central Gulf Coast will escort a=20   
   plume of Gulf moisture northeastward into a frigid air-mass of=20   
   early December. Overrunning moisture along a narrow 925-850mb front   
   from central AR on east to the southern Appalachians is set to=20   
   give rise to a potentially disruptive wintry mix. Ice accumulations   
   from the Little Rock-Memphis-Nashville metro areas will be light,=20   
   but given it is the first icing setup of the season, untreated=20   
   roads may become slick and treacherous for travelers, especially=20   
   for the Thursday PM rush hour and overnight Thursday.=20   
      
   As the upper trough approaches the Mid-Atlantic Thursday night,=20   
   enhanced 290K isentropic ascent and increasing 850-700mb WAA aloft=20   
   will foster periods of snow to develop from the central=20   
   Appalachians and Blue Ridge of WV/VA on east across the=20   
   central/southern VA Piedmont Thursday night and into Friday=20   
   morning. Similar to the Mid-South, this will be the first=20   
   accumulating snow of the season, likely resulting in hazardous=20   
   travel conditions on untreated surfaces. Farther south, an icy=20   
   over-running setup looks to unfold from the southern Appalachians=20   
   on east across northern NC. A wintry mix is likely to cause some=20   
   minor ice accumulations on roads, sidewalks, and vegetation Friday=20   
   morning and could cause travel delays.   
      
   WPC probabilities show moderate chances (40-60%) for snowfall=20   
   totals >2" from the Central Appalachians to south-central VA, which   
   does include portions of the Richmond, VA metro area. Localized   
   amounts topping 4" are possible in the Blue Ridge Mountains of   
   southwest VA. In terms of ice accumulations, most areas from the   
   Mid-South to the Mid-Atlantic can expect ice accumulations less   
   than a tenth of an inch, although some of the southern Appalachians   
   of NC could see localized amounts approach one-tenth. The WSSI does   
   depict localized areas of Minor Impacts through Friday.   
      
      
   ...Pacific Northwest, Northern & Central Rockies...   
   Days 1-3...   
      
   A highly active storm track into the Northwest will usher in   
   copious amounts of Pacific moisture from the Pacific Northwest on   
   east into the Northern and Central Rockies. Starting today, a   
   steady barrage of >90th climatological percentile PWATs will stream   
   across the Pacific Northwest and will over into the Great Basin=20   
   and Rockies through Friday and linger into Saturday. Synoptic-scale   
   forcing will be present throughout the Northern Rockies through=20   
   Friday, then over the Central Rockies late Friday into Saturday as   
   a stubborn NW-SE oriented 250mb jet streak places its diffluent=20   
   left-exit region overhead. Snow levels over the Pacific Northwest=20   
   will dip as low as 3,000ft while the Northern Rockies generally=20   
   hover around 4,000ft. As height falls ensue on Friday and continue   
   into Saturday, snow levels will drop to as low as 2,000ft,=20   
   although the heaviest snowfall will be confined to elevations above   
   5,000ft in the Bitterroots, Lewis Range, and Sawtooth, above=20   
   6,000ft in the Tetons, Absaroka, Big Horns, Bear River, and Wasatch   
   Ranges, and above 7,000ft in the central WY/CO Rockies.=20   
      
   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. Over the next few days, WPC   
   probabilities paint a wintry picture across many of the Northern   
   and Central Rockies, as well as the higher elevations of the=20   
   Cascades (above 5,000ft) with high chances (>70%) for snowfall   
   totals >12" in all of these listed ranges and elevations through   
   Saturday. In fact, the higher elevations of the Lewis Range,   
   Bitterroots, and Tetons have moderate-to-high chances (50-80%) for   
   snowfall totals >24". The WSSI shows many areas of Minor Impacts=20   
   of the Northern and Central Rockies, including some Moderate to=20   
   locally Major Impacts. The Major Impact potential areas=20   
   (considerable disruptions; dangerous travel and widespread=20   
   closures) along the Wasatch east of Salt Lake City. Residents in=20   
   these mountain ranges should prepare for a multi-day stretch of=20   
   winter weather that results in difficult and treacherous travel=20   
   conditions.   
      
   ...Midwest...   
   Day 3...   
      
   The active pattern of Pacific moisture and disturbances traversing   
   the Northwest will result in at least one of these disturbances   
   reaching the Midwest late Friday night and into Saturday. A general   
   model consensus agrees a slug of rich Pacific moisture within the   
   700-300mb layer will advance across the northern Great Plains and   
   reach the Missouri River Valley by Saturday. This is where the   
   agreement in guidance ends, however, as individual guidance members   
   (including ensembles) disagree upon the strength and track of this=20   
   storm as it reaches the Central Plains on Saturday. The synoptic-=20   
   scale setup should foster an 850mb low with sufficient 850-700mb=20   
   FGEN to give rise to a band of moderate-to-heavy snow, but exactly=20   
   where this band sets up is low confidence.=20   
      
   At the moment, WPC probabilities show minor snowfall totals (1-3")   
   generally having moderate-to-high chances (30-50%) across the=20   
   northern High Plains through Saturday morning. The high degree of=20   
   spread in model solutions is causing WPC probabilities to sport low   
   chances (10-30%) for snowfall totals >4" from southeast SD and=20   
   northeast NE on east through southern MN and northern IA. That=20   
   being said, the favorable synoptic and mesoscale processes at play=20   
   could very much support a band of >6" snowfall totals that causes=20   
   travel headaches for residents in the Midwest. Those in the Midwest   
   should continue to monitor the forecast closely as more snow is in   
   the forecast and is likely to cause some travel headaches (WSSI-P=20   
   shows 40-60% chances for Minor Impacts from southeast SD and=20   
   northeast NE on east through southern MN and northern IA) but=20   
   details as to which areas are likely to see the worst impacts are=20   
   still unclear at this time.   
      
   Mullinax   
      
      
   ...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!-wJ58ymkpysFxygKi1ghMuAJzz62G2BeQhLjLlRE1QtRe=   
   gwW2cnJ4DMLjWxp4ol_eRJ292Trto_NlWn0sb-kn78UBsc$=20   
      
      
      
   $$   
      
   =3D =3D =3D   
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