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   FOUS11 KWBC 090734   
   QPFHSD   
      
   Probabilistic Heavy Snow and Icing Discussion   
   NWS Weather Prediction Center College Park MD   
   234 AM EST Mon Feb 9 2026   
      
   Valid 12Z Mon Feb 09 2026 - 12Z Thu Feb 12 2026   
      
      
   ...Pacific Northwest through Northern Rockies...   
   Day 1...   
      
   A shortwave trough crossing the area will be positioned atop the   
   interior Northwest to start the period, and then translate rapidly   
   eastward through D1. This feature will likely shear out into the   
   westerlies as it advects into the High Plains in response to rapid   
   ridging building in its wake, but there has been a subtle trend of   
   increased amplitude of this feature tonight. This shortwave will   
   work effectively with an intensifying upper jet streak to overlap   
   mid-level height falls with LFQ diffluence, leading to sufficient   
   ascent to produce a wave of low pressure along a cold front south   
   of the region.   
      
   Additionally, this jet streak will result in increasing mid-level   
   frontogenesis, especially within the 700-500mb layer, which will   
   produce impressive omega directly into the DGZ. Although ascent   
   will be temporally modest, cross-sections indicate a high threat   
   for CSI within any snow bands that develop, and this could (30-60%   
   chance) produce 1-2"/hr snowfall rates. The heaviest snowfall is   
   likely in the terrain of the Absarokas and near Yellowstone NP due   
   to upslope enhancement, but anywhere across southern MT and   
   northern WY could see bands of heavy snowfall which will accumulate   
   rapidly despite marginal thermals in the low- levels. The high-res   
   guidance has trended upward significantly, as have many of the   
   globals, so confidence has increased in significant snowfall   
   accumulations, which is now reflected by WPC probabilities that   
   indicate a high risk (>70% chance) for at least 4 inches, with more   
   than 12 inches possible in the higher terrain including the Lewis   
   Range and Tetons.   
      
      
   ...Sierra Nevada to the Central Rockies...   
   Days 2-3...   
      
   A closed mid-level low will approach central California from the   
   west on Tuesday before slowly filling into an open, positively   
   tilted trough Wednesday as secondary vorticity energy digs towards   
   Baja. This slow evolution will result in pronounced S/SW flow   
   aloft, which will combine with a strengthening jet streak to spread   
   moisture onshore CA and then expand eastward towards the Central   
   Rockies by late Wednesday. This prolonged, albeit relatively   
   modest, moisture plume/IVT will bring much needed precip to the   
   Great Basin and central Rockies through midweek.   
      
   Snow levels will be at or just below 7000ft along the Sierra Nevada   
   on Tuesday in the onshore flow, dropping to around 6000ft Tuesday   
   night under height falls. Great Basin/Rockies snow levels will   
   generally remain 6000-7000ft through midweek.   
      
   2-day snow probabilities from WPC suggest a near certainty (>90%)   
   of at least 8 inches across much of the Sierra with locally as much   
   as 2 feet possible (30% chance) in the higher Sierra. Additional   
   snowfall totals exceeding 8 inches are possible (50-70%) for parts   
   of the Uintas, Colorado Rockies, and northern CA ranges.   
      
      
   ...Northern Great Lakes and Northeast...   
   Days 1-3...   
      
   A closed mid-level low will elongate and track from the Northern   
   Great Lakes to across New England mid-week, exiting to the Gulf of   
   Maine by Thursday morning. This upper feature will be accompanied   
   by an extended vorticity lobe on its south side, helping to produce   
   strong ascent through height falls/PVA across the region. As this   
   develops, pronounced warm air advection (WAA) will develop to its   
   south as a surface low /clipper type/ races southeast beneath the   
   upper trough. This will produce two rounds of ascent: first with   
   the intensifying WAA south of the surface low, and then second with   
   post-clipper CAA/upslope flow.   
      
   While the ascent within the WAA will be impressive, it will also be   
   of short duration, generally 6-12 hours, so although snowfall rates   
   will likely be intense (50-70% chance of 1+"/hr), the total   
   snowfall accumulations will be tempered as reflected by WPC   
   probabilities that are around 30% for 4+ inches across the U.P. of   
   MI D1, and then 30-70% on D2 for Upstate NY and northern/central   
   New England. Despite that, some more significant snowfall   
   accumulations are likely across the Tug Hill Plateau, the   
   Adirondacks, and the Greens where a combination of CAA for lake   
   effect snow (in the Tug Hill) and upslope snow (Adirondacks and   
   Greens) will lengthen the duration of accumulating snowfall. In   
   these areas, locally more than 8 inches of snow is possible   
   (10-30%, highest across the Tug Hill Plateau).   
      
   Finally, as the closed low moves into the Gulf of Maine, a surface   
   low will deepen offshore in response. While direct impacts from   
   this surface low are not expected to be significant, the guidance   
   is hinting at a lingering inverted trough pivoting back across   
   coastal Maine Wednesday. These inverted troughs can sometimes lead   
   to sneaky-heavy snowfall accumulations, so although current WPC   
   probabilities are around 50-70% for 4+ inches of snow, this will   
   need to be monitored for any upticks as the event gets closer.   
      
      
   Weiss   
      
      
   $$   
      
   = = =   
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