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   FOUS11 KWBC 050815   
   QPFHSD   
      
   Probabilistic Heavy Snow and Icing Discussion   
   NWS Weather Prediction Center College Park MD   
   315 AM EST Fri Dec 5 2025   
      
   Valid 12Z Fri Dec 05 2025 - 12Z Mon Dec 08 2025   
      
      
   ...Great Lakes...   
   Days 1-2...   
      
   Periodic mid/upper level impulses rotating within a broad cyclonic   
   flow pattern will continue to support rounds of light-to-moderate   
   lake effect snowfall across the upper Great Lakes through Saturday.   
   Friday features modest WAA over the Great Lakes via SWrly flow that   
   looks to produce periods of snow over the northwestern towns of   
   Michigan's Mitten, while a cold frontal passage on Saturday   
   revitalizes LES bands over the Michigan U.P. and downwind of Lake   
   Ontario over the Tug Hill. WPC probabilities show low-to-moderate   
   chances (30-60%) for snowfall totals >4" over northwest mainland   
   Michigan today. By Saturday, most snowfall totals over the eastern   
   Michigan U.P. and downwind of Lake Ontario is likely to range   
   between 1-4".   
      
      
   ...Mid-Atlantic...   
   Day 1...   
      
   The first winter hazards of the season for much of the Mid-   
   Atlantic is unfolding this morning. As weak low pressure slides   
   eastward over the Southeast, enhanced 290K isentropic ascent,   
   increasing 850-700mb WAA aloft, and strengthening low-level frontogenesis   
   is producing periods of snow from the central Appalachians and   
   Blue Ridge of WV/VA on east across the central/southern VA Piedmont   
   and across the DelMarVa Peninsula. Light snow is advancing as far   
   north as the Washington D.C./Baltimore metro areas, which is   
   may result in slick roads for the Friday AM commute. This will be   
   the first accumulating snow of the season, likely resulting in   
   hazardous travel conditions on untreated surfaces across much of   
   the Mid-Atlantic. Farther south, an icy overrunning setup looks to   
   unfold from the southern Appalachians on east across northern NC.   
   A wintry mix is likely to cause some minor ice accumulations on   
   roads, sidewalks, and vegetation Friday morning and could cause   
   travel delays. Snow should taper off by mid-afternoon with   
   lingering icy conditions across affected areas of the Mid-Atlantic   
   through Friday night.   
      
   Snowfall accumulations are likely to range between 1-4" from   
   southern WV and southwest VA across southern VA (including the   
   Richmond metro area) and into the lower DelMarVa Peninsula.   
   Localized totals >4" are possible in the Blue Ridge Mountains of   
   southwest VA. In terms of ice accumulations, most areas from the   
   VA/NC Blue Ridge on east across southern VA and northern NC can   
   expect minor 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 Minor Impacts through   
   Friday afternoon for most areas referenced in this discussion with   
   some localized Moderate Impacts in the southern VA Piedmont.   
      
      
   ...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. A steady barrage of   
   >90th climatological percentile PWATs will stream across the   
   Pacific Northwest into the Great Basin and Rockies today, with   
   another round of >90th percentile PWATs arriving in the Pacific   
   Northwest on Sunday. Synoptic-scale forcing will be located over   
   the Northern Rockies today, then over the Central Rockies Friday   
   night into Saturday as a persistent NW-SE oriented 250mb jet   
   streak places its diffluent left exit region overhead. Snow levels   
   over the Pacific Northwest will dip as low as 3,000ft while the   
   Northern Rockies generally hover around 4,000ft. As height falls   
   transpire today over the Northwest and continue through Saturday,   
   snow levels will drop to as low as 2,000ft, although the heaviest   
   snowfall will be confined to elevations above 5,000ft in the   
   Bitterroots, Lewis Range, and Sawtooth, above 6,000ft in the   
   Tetons, Absaroka, Big Horns, Bear River, and Wasatch Ranges, and   
   above 7,000ft in the central WY/CO Rockies. Snow looks to taper off   
   across the Central Rockies by Saturday evening, but the next   
   atmospheric river will deliver another plume of Pacific moisture   
   across the Pacific Northwest and northern Rockies on Sunday.   
      
   WPC probabilities are impressive Day 1 and 2 across the higher   
   terrain from Glacier NP through Yellowstone NP including portions   
   of the Sawtooth/Salmon River ranges, Absarokas, terrain of NW WY,   
   northern Utah, and into the Park Range of CO. Here, WPC   
   probabilities Day 1 and 2 reach above 70% for 8+ inches, and Day 1   
   and Day 2 snowfall could be impressive above generally 6000 ft   
   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   
   Cascades (above 5,000ft) with high chances (>70%) for additional snowfall   
   totals >18" 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". Moderate to heavy snow continues into Day 3   
   over the WA Cascades and northern Rockies, though probabilities   
   suggest less snowfall compared to the more snowy stretches on   
   Friday and Saturday. The WSSI shows many areas of Minor and   
   Moderate Impacts across the Northern and Central Rockies,   
   including some locally Major Impacts. The Major Impact potential   
   areas (considerable disruptions; dangerous travel and widespread   
   closures) include areas along the Wasatch east of Salt Lake City   
   and the more remote areas of these Intermountain West ranges.   
   Residents in these mountain ranges should prepare for a multi-day   
   stretch of winter weather that results in difficult and treacherous   
   travel conditions.   
      
   ...Northern Plains & Midwest...   
   Days 2-3...   
      
   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 into Saturday. 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. The synoptic-scale setup favors the development   
   of an 850mb low with sufficient 850-700mb FGEN and WAA to the north   
   and east of the 850mb low track to support a band of moderate-to-   
   heavy snow. The band of snow starts out Saturday morning across   
   the Dakotas, then heads for southern MN and northern IA by late   
   Saturday afternoon and evening, and begins to weaken in intensity   
   by early Sunday morning the snow reaches the Lower Great Lakes and   
   OH Valley.   
      
   The latest WPC probabilities have increased with this forecast,   
   now supporting probabilities of 50-70% for snowfall totals >4" for   
   locations that banding (mentioned above) is most likely across the   
   Midwest. However, given the favorable synoptic and mesoscale   
   processes at play, a band of >6" snowfall totals that cause travel   
   headaches for residents in the Midwest is very much on the table,   
   as evident in the low-to-moderate chances (20-50%) for snowfall   
   totals >6" over northern IA. Those in the Midwest should continue   
   to monitor the forecast closely as additional changes in the   
   placement and totals of the heaviest snowfall could still change   
   over the next 24 hours.   
      
   ...Northeast...   
   Day 3...   
      
   There remains a good deal of uncertainty in the forecast   
   on Sunday with the GFS remaining aggressive in a more   
   amplified/phase solution compared to the ECMWF/CMC. The GFS is also   
   noticeably wetter than the GEFS over the Northeast. The ECMWF/CMC   
   camp shows a broader and less amplified 500mb trough over the Great   
   Lakes and southeast Canada, but enough 500mb PVA and lake-enhanced   
   snowfall bands are showing low chances (10-30%) for snowfall   
   totals >4" downwind of Lakes Erie and Ontario. Some minor impacts   
   to travel are possible as denoted by the WSSI-P showing low-to-   
   moderate chances (30-60%) for Minor Impacts on Sunday.   
      
   Mullinax   
      
      
      
      
   $$   
      
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