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   FOUS11 KWBC 051907   
   QPFHSD   
      
   Probabilistic Heavy Snow and Icing Discussion   
   NWS Weather Prediction Center College Park MD   
   207 PM EST Mon Jan 5 2026   
      
   Valid 00Z Tue Jan 06 2026 - 00Z Fri Jan 09 2026   
      
      
   ...Upper Midwest/Great Lakes/Northeast...   
   Days 1-3...   
      
   A progressive shortwave trough over southern Ontario is producing   
   weak PVA over the Northeast, along with minor 850-700mb WAA ahead   
   of the trough. Sufficient 850-300mb moisture is present to support   
   periods of light-to-moderate snow over the Northeast this afternoon   
   and evening, but snow should taper off not long after midnight.   
   Minor snowfall accumulations of 1-4" are expected with some slick   
   conditions on untreated surfaces possible.   
      
   As the trough in the Northeast exits east into the North Atlantic   
   tonight, another disturbance with Pacific origins follows on its   
   heels as it develops a wave of low pressure in the Midwest. Located   
   beneath the divergent left-exit region of a 150kt 250mb jet streak,   
   the storm will gradually strengthen at the same time as 850-700mb   
   WAA ahead of the low also increases. While this disturbance is   
   similar to the one over the Northeast in that it is progressive,   
   there will be a stronger warm nose aloft that makes ice the primary   
   concern over the Midwest and Great Lakes this time around. An icy   
   wintry mix is beginning over parts of the eastern Dakotas and   
   central MN this afternoon, but as WAA increases, so will the rates   
   of sleet and freezing rain. Look for icy conditions to unfold   
   across WI and over MI's U.P. (Upper Peninsula) tonight, then over   
   MI's L.P. (Lower Peninsula) by Tuesday morning. The wintry mix may   
   linger over the Great Lakes and Midwest through midday Tuesday, but   
   should taper off by Tuesday evening, meaning there could still be   
   lingering icy conditions for the Tuesday afternoon rush hour. WPC   
   probabilities show at least moderate chances (>50%) for ice   
   accumulations over one-tenth of an inch of ice from southern MN to   
   northern MI. The WSSI shows a large swath of at least Minor   
   Impacts (slick travel conditions possible, use caution) from   
   southern MN on east through northern WI and into central MI. There   
   is an area denoting Moderate Impacts (hazardous travel conditions,   
   closures possible) in the heart of WI where localized ice   
   accumulations could approach one-quarter inch.   
      
   As the storm tracks over southern MI Tuesday afternoon, the same   
   synoptically-forced mechanisms aloft will support periods of snow   
   over the Adirondacks and northern New England. Farther south, a   
   wintry mix of sleet and freezing rain will envelope central NY,   
   northern NJ, and northeast PA starting as early as Tuesday   
   afternoon, then advance east into the heart of New England with the   
   Green Berkshires, and Worcester Hills Tuesday night. Throwing a   
   wrench into the forecast is the expected development of a coastal   
   low along a coastal front off southern New England. This transition   
   from the primary low over southern Ontario to the new coastal low   
   off the MA Capes will be pivotal in how long central New England   
   stays a wintry mix and when/if they transition to snow. Northern   
   Maine and the White Mountains have the greater chances of seeing   
   snow as their primary precip type for this event Tuesday night and   
   into Wednesday morning. Through the daytime hours Wednesday, an icy   
   wintry mix is likely to linger over coastal ME but all   
   precipitation tapers off by Wednesday evening.   
      
   WPC probabilities show high chances (>70%) for ice accumulations   
   >0.01" over the Catskills, Adirondacks, and much of interior New   
   England. The Adirondacks, Berkshires, Green, and Worcester Hills   
   have moderate chances (40-60%) for ice accumulations over one-tenth   
   of an inch. In terms of snowfall, the tallest peaks of the   
   Adirondacks, northern Greens, Whites, and northern ME show moderate   
   chances (40-60%) for snowfall over 2" through Wednesday evening,   
   but should the coastal low strengthen faster, localized snowfall   
   totals of 4-6" could transpire in northern ME. WSSI shows these   
   winter hazards generally look to cause Minor Impacts, indicating   
   the potential for some areas of hazardous travel due to snow and   
   ice Tuesday night and through Wednesday.   
      
      
   ...Olympics, Cascades, and Northern/Central Rockies...   
   Days 2-3...   
      
   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   
   enhanced polar jet will direct a potent IVT that ranges between   
   250-500 kg/m/s at the Pacific NW, while at the same time, being   
   co-located beneath the divergent left-exit region of the   
   aforementioned 250mb jet streak. While moisture content is not   
   overly anomalous, the westerly IVT supporting enhanced upslope   
   flow, falling mid-upper level heights, and supportive jet streak   
   dynamics will support rounds of heavy mountain snow over the   
   Cascades and Olympics. 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 Tuesday afternoon, 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.   
      
   With snow 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. Current WSSI shows Moderate Impacts at these passes   
   (hazardous travel, potential closures) but given the higher end   
   snowfall potential, the WSSI-P does depict a scenario (20-30%   
   potential) for Major Impacts that would imply more dangerous travel   
   conditions. Regardless, multiple days of heavy snowfall is   
   expected, so passes will likely contend with prolonged delays and   
   potential closures.   
      
   The Pacific moisture spills east into the Northern Rockies as well   
   through the first half of the week. There is already lingering   
   Pacific moisture leftover from the heavy rainfall and mountain snow   
   in CA that is supporting periods of snow today and into tonight in   
   the Sawtooth, Bitterroots, Tetons, Wind River, and as far south as   
   the more remote reaches of the CO Rockies. As Pacific moisture   
   arrives Tuesday afternoon thanks to 250 kg/m/s IVT extending as far   
   east as eastern WA, periods of heavy snow ensue above 4,000ft in   
   the northern Bitterroots, above 5,000ft in the Lewis Range, Blue,   
   and Sawtooth Mountains, and above 7,000ft in the Absaroka, Tetons,   
   and Bear River Ranges. WPC probabilities over the next 72-hours   
   show high chances (>70%) for over 12" of snow in these ranges with   
   moderate chances (>50%) for snowfall eclipsing 24" in the more   
   remote elevations of the Bitterroots, Sawtooth, Tetons, and Wind   
   River ranges. The peaks of the Tetons sport the best odds of seeing   
   localized snowfall totals over 3 feet.   
      
   By Wednesday evening, attention turns to the central Rockies where   
   they will be placed ahead of two approaching shortwave troughs; one   
   diving south and east from the Pacific NW and another approaching   
   from northwest Mexico. As the former disturbance deepens Wednesday   
   night and into Thursday, periods of mountain snow are likely to   
   envelope the Wasatch, Uinta, all of the CO Rockies, and even as far   
   south as the Mogollon Rim and the Rockies of NM. Guidance shows a   
   fair amount of uncertainty in the handling of these two features,   
   so confidence in totals remains low. That said, the pattern support   
   accumulating mountains snow (generally above 7,000ft) Wednesday   
   night and into Tuesday. Residents along the Front Range of the   
   CO/WY/NM Rockies will want to monitor the forecast closely as this   
   could result cause impacts to travel and commerce late week.   
      
      
   Mullinax   
      
      
      
      
      
   $$   
      
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