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   FOUS11 KWBC 060751   
   QPFHSD   
      
   Probabilistic Heavy Snow and Icing Discussion   
   NWS Weather Prediction Center College Park MD   
   251 AM EST Tue Jan 6 2026   
      
   Valid 12Z Tue Jan 06 2026 - 12Z Fri Jan 09 2026   
      
      
   ...Great Lakes & Northeast...   
   Days 1-2...   
      
   Amplifying shortwave will move steadily eastward from the Great   
   Lakes tonight, passing off the New England coast Wednesday morning.   
   While the flow in which this impulse will be embedded is generally   
   zonal, some modest amplification is progged by the consensus, with   
   the subsequent height falls overlapping modest LFQ diffluence from   
   a jet streak to the south to enhance deep layer lift, especially in   
   the Northeast. This will likely result in two waves of surface low   
   pressure: one moving from MI into Ontario, with secondary   
   development occurring off the coast of Maine. The speed at which   
   this second low develops, as well as its latitude, will have a   
   strong influence on how much cold air can lock in across New   
   England within the in-situ wedge. While the trends in the guidance   
   continue to be a slightly farther south and stronger offshore low,   
   which will enable more cold air to lock in, mixed precip is still   
   likely to be the dominant p-type outside of the higher terrain and   
   across northern New England. This system should remain progressive   
   as well, limiting total impacts and amounts.   
      
   For areas that receive mostly snow (the Adirondacks and northern   
   New England) WPC probabilities for 4+ inches of accumulations are   
   modest at 10-30%, but locally reach as high as 50% in NH and ME. South   
   of there, a mix including freezing rain is likely, which could   
   produce more than 0.1" of ice (30-50% chance) highest in the   
   Greens, Berkshires, and Worcester Hills.   
      
      
   ...Olympics, Cascades, and Northern/Central Rockies...   
   Days 1-3...   
      
   A powerful storm system over southern AK will work in tandem with   
   an unusually strong subtropical ridge north of HI to create a   
   robust 160kt 250mb jet streak in the northeast Pacific. This   
   will transport potent IVT eastward within pinched but generally   
   zonal flow, reflected by GEFS probabilities that exceed 80% for 250   
   kg/m/s, but are less than 25% for 500 kg/m/s. This increasing   
   moisture, while not exceptional, will be wrung out efficiently by   
   PVA within shortwaves traversing the flow, the LFQ of a slowly   
   sinking but strengthening Pacific jet streak, and persistent, at   
   times continuous, upslope flow, especially in the Olympics and   
   Cascades. Snow levels will fall to as low as 2,000ft, although the   
   heavier and more impactful snow will be observed above 3,000ft.   
   The heaviest snowfall arrives D1, and following a brief break in   
   the heavier snowfall rates early Wednesday morning, another   
   disturbance arrives later in the day with more snow in the Cascades   
   and Olympics. This time, with a colder air-mass aloft, snow levels   
   dip to as low as 1,000ft Wednesday afternoon and continuing into   
   Thursday. Although snow levels remain generally at or above 1,000   
   ft, steepening lapse rates aloft with continued ascent could result   
   in locally lower snowfall, reflected by the NBM 10th percentile   
   snow level falling to around 600 ft. While this should still   
   prevent significant accumulations in the lowlands, some of the   
   foothills west of the Cascades could see light snowfall on D2 as   
   well.   
      
   With snow nearly continuously falling in these ranges through   
   Thursday, WPC's 72-hour snowfall probabilities are quite impressive   
   with high chances (>70%) for snowfall totals >24" above 3,000ft in   
   the Cascades and Olympics, including passes such as Snoqualmie and   
   Stevens. At the higher elevations, 4-6 feet of snow is possible.   
   This snowfall, despite elevated SLRs as the column cools, will   
   result in dangerous travel across most Cascade Passes, with the   
   WSSI-P indicating a moderate threat (50-70%) of major impacts   
   through the Cascades. Motorists should prepare for dangerous travel   
   and potential pass closures this week.   
      
   Farther east into the Northern Rockies and then pivoting down to   
   the Central Rockies, spokes of energy within the generally zonal   
   flow will provide sufficient ascent to wring out moisture that   
   spills across the Cascades. Although snowfall farther east should   
   be somewhat less impressive than points west, WPC probabilities for   
   12+ inches during the next 3 days are high (>90%) in the higher   
   terrain from the Blue Mountains of OR through most of the Northern   
   Rockies, and down through the Tetons, Wind Rivers, and parts of the   
   Wasatch. Locally, 2-4 feet is possible in the highest peaks of   
   these ranges, and pass-level travel will also be significantly   
   impacted this week.   
      
      
   ...Four Corners States...   
   Day 3...   
      
   Shortwave digging southeast from the Pacific Northwest will amplify   
   rapidly as it approaches the Central Rockies, potentially closing   
   off over the CO/NM High Plains Thursday night. There continues to   
   be a lot of spread in the mid-level evolution leading to lower than   
   typical confidence by D3, however, the cluster analysis (from 00Z/5   
   which is the most recent available) suggests there is potential for   
   continued deepening due to more pronounced upstream ridging leading   
   to a deeper trough (supported by more than 60% of the members,   
   although many of these are from the CMCE which may be somewhat   
   under-dispersive at this time). However, the trends in the   
   incoming 00z suite suggest the trough continues to be deeper, which   
   may result in a more substantial winter weather event.   
      
   As the guidance has trended steadily slower and faster with this   
   feature, suggesting more impressive deep layer ascent, the   
   resulting downstream jet streak has also intensified and arced   
   more impressively poleward. As this jet arcs northward, the   
   overlap of LFQ diffluence with height falls will likely lead to lee   
   side cyclogenesis Thursday evening, within a column that, while   
   will feature generally normal to below normal PWs, will saturate in   
   response to increasing low- level easterly flow around the   
   strengthening surface low. With steep lapse rates aloft helping to   
   cool the column, and flow becoming increasingly favorable to   
   upslope into the terrain, at least light snow is becoming likely   
   for much of the terrain and into the High Plains of CO/NM,   
   including the I-25 metro which has experienced a relative dearth of   
   snowfall so far this season. While adjustments in the forecast are   
   likely, current WPC snow probabilities indicate a high risk (>70%   
   chance) for 4+ inches of snow across much of the CO Rockies,   
   including the Front Range, and portions of the Wasatch, and down to   
   the White Mountains of AZ. The lower elevations of I-25 and into   
   the High Plains have a 10-30% chance of 4+ inches, although locally   
   higher amounts are possible across the Palmer Divide and Raton   
   Mesa.   
      
      
   Weiss   
      
      
   $$   
      
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