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   FOUS11 KWBC 042010   
   QPFHSD   
      
   Probabilistic Heavy Snow and Icing Discussion   
   NWS Weather Prediction Center College Park MD   
   310 PM EST Thu Dec 4 2025   
      
   Valid 00Z Fri Dec 05 2025 - 00Z Mon Dec 08 2025   
      
      
   ...Great Lakes...   
   Days 1-3...   
      
   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 the next few   
   days. WPC probabilities continue to show low-to-moderate chances   
   (30-60%) for snowfall totals >4" each day Friday through Sunday,   
   primarily across eastern portions of the U.P. of Michigan as well   
   as northern parts of Michigan's Mitten. Slightly higher   
   probabilities for lower snowfall amounts exist downwind of Lake   
   Erie and Lake Ontario on Sunday.   
      
      
   ...Mid-South to the Mid-Atlantic...   
   Day 1...   
      
   The first winter hazards of the season from the Mid-South to the   
   Mid-Atlantic continue tonight into Friday as a developing wave of   
   low pressure along the central Gulf Coast escorts a plume of Gulf   
   moisture northeastward into a frigid air-mass for early December.   
   Overrunning moisture along a narrow 925-850mb front from central AR   
   on east to the southern Appalachians is set to give rise to a   
   potentially disruptive wintry mix. Ice accumulations from the   
   Little Rock-Memphis-Nashville metro areas will be light, but given   
   it is the first icing setup of the season, untreated roads may   
   become slick and treacherous for travelers through the overnight   
   hours tonight.   
      
   As weak low pressure slides eastward along the Gulf Coast,   
   enhanced 290K isentropic ascent, increasing 850-700mb WAA aloft,   
   and strengthening frontogenesis will foster periods of snow to   
   develop from the central Appalachians and Blue Ridge of WV/VA on   
   east across the central/southern VA Piedmont tonight and into   
   Friday morning. Latest trends also suggest the northern extent of   
   the snow shield likely reaching into the Baltimore/Washington   
   Metros late tonight into early Friday morning. Similar to the Mid-   
   South, this will be the first accumulating snow of the season,   
   likely resulting in hazardous travel conditions on untreated   
   surfaces. 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.   
      
   WPC probabilities have increased with this forecast package, now   
   showing moderate to high chances (50-90%) for snowfall 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   
   and southern WV. 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. A steady barrage of   
   >90th climatological percentile PWATs will stream across the   
   Pacific Northwest into the Great Basin and Rockies Friday into   
   Sunday. Synoptic-scale forcing will be present throughout the   
   Northern Rockies through Friday, then over the Central Rockies late   
   Friday 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   
   ensue on Friday and continue Saturday into Sunday, 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.   
      
   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 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".   
   Moderate to heavy snow continues into Day 3, though probabilities   
   are less compared to Days 1 and 2. The WSSI shows many areas of   
   Minor Impacts of the Northern and Central Rockies, including some   
   Moderate to locally Major Impacts. The Major Impact potential areas   
   (considerable disruptions; dangerous travel and widespread   
   closures) along the Wasatch east of Salt Lake City. Residents in   
   these mountain ranges should prepare for a multi-day stretch of   
   winter weather that results in difficult and treacherous travel   
   conditions.   
      
      
   ...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 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. While the latest   
   models still disagree somewhat on the strength and track of this   
   storm as it reaches the Central Plains on Saturday and then the   
   Upper Midwest Saturday night into Sunday, the synoptic-scale setup   
   should foster an 850mb low with sufficient 850-700mb FGEN to give   
   rise to a band of moderate-to-heavy snow. Right now, this appears   
   to be most likely from southeast South Dakota and northeast   
   Nebraska to southwest Minnesota and northwest Iowa.   
      
   The latest WPC probabilities have increased with this forecast,   
   now supporting 48-hour (Days 2-3) probabilities of 30-70% for   
   snowfall totals >4" for locations that banding (mentioned above) is   
   most likely. Additionally, 48-hour probabilities of >8", while low   
   (10-15%) are non-zero across southwest Minnesota and northwest   
   Iowa, suggesting that the favorable synoptic and mesoscale   
   processes at play could very much support a band of >6" snowfall   
   totals that cause travel headaches for residents in the Midwest.   
   Those in the Midwest should continue to monitor the forecast   
   closely as additional increases in probabilities are possible with   
   future forecast packages.   
      
      
   Miller/Mullinax   
      
      
      
      
      
   $$   
      
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