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   FOUS11 KWBC 150723   
   QPFHSD   
      
   Probabilistic Heavy Snow and Icing Discussion   
   NWS Weather Prediction Center College Park MD   
   223 AM EST Sat Nov 15 2025   
      
   Valid 12Z Sat Nov 15 2025 - 12Z Tue Nov 18 2025   
      
      
   ...California...   
   Days 1-3...   
      
   A pair of upper lows are forecast to impact much of the central and   
   southern Sierra Nevada with heavy snow over the next few days. The   
   first upper low is expected to situate off the coast of southern   
   California to start the period. This system will also be   
   particularly deep early Saturday, with 500mb heights around the   
   0.5th climatological percentile over the eastern Pacific per the   
   18z ECMWF. This closed upper low is forecast to swing inland during   
   the day 1 period while also weakening. This will provide a surge   
   of moist southerly flow into the central/southern Sierra. This flow   
   will not be ideally orthogonal to the Sierra off the Pacific, but   
   the upper low placement overhead and PWs near the climatological   
   maximum for November (per the NAEFS) will allow for gradually   
   falling snow levels, ample lift, and widespread moderate   
   precipitation. Snow levels will once again start out above 9k feet,   
   but gradually fall to around 7k feet by Sunday morning ahead of   
   another rapidly approaching upper low early Monday. This second   
   upper low is expected to be rather progressive, but could contain   
   IVT above 400 kg/m/s for a brief period of time oriented primarily   
   into the central Sierra Nevada. In total, an additional 1-2 feet of   
   snowfall (and even up to 3 feet locally in portions of the   
   southern Sierra) is possible above 8k feet elevation.   
      
   The latest WPC 72-hr snow probabilities >24" across the high   
   terrain of southern Sierra Nevada remain very high (80-99%) above   
   9k feet, and moderate (40-60%) above 8k feet.   
      
      
   ...Interior Northeast...   
   Days 1-3...   
      
   Persistent troughing remains across New England and southeast   
   Canada to start the period and will be reinforced by a potent   
   shortwave dropping southeast into the region by Sunday before   
   deepening into a strong vertically stacked low through the end of   
   day 2. This will provide for warm air advection driven   
   precipitation Saturday night into Sunday as cold low-level air   
   ahead of this system produces a CAD setup across northern New   
   England, with strong cold air advection returning across the   
   Northeast on days 2 and 3. The associated surface low is forecast   
   to slide from southeast Ontario to coastal Maine and allow for the   
   low- level cold air to only very slowly retreat north. A wintry mix   
   with pockets of freezing rain is most likely to impact the   
   Adirondacks into the Green and White Mts of VT/NH/ME, beginning as   
   early as Saturday evening after a brief period of moderate to heavy   
   snow. As the surface low matures near southeast ME, deformation   
   banding within a developing trowal is possible across northern ME   
   and could produce pockets of 1"/hr snowfall rates on Sunday.   
      
   The transient nature of the WAA should limit the ice threat   
   somewhat. For this region, WPC 24-hr probabilities (12z Sat - 12z   
   Sun) for at least 0.1" of ice generally range between 40-70%   
   (though are now as high as 75-95% for portions of the Adirondacks   
   in Essex County) and low chances (<30%) for more than 0.25". This   
   is still enough freezing rain to cause slippery untreated roads   
   and sidewalks. Snowfall will remain the predominant precip type   
   across far northern NY, VT, NH and into central/northern ME where   
   QPF may also be limited enough to prevent a major snowfall event,   
   but some heavier snowfall rates are possible with the initial   
   precipitation onset when 700 mb fgen is strongest and the mid-level   
   low crosses over the region. WPC probabilities for at least 8" are   
   between 30-50% in this region through Day 2, and locally are as   
   high as 80% across portions of the northern Greens/Whites and   
   northern ME where CAA upslope helps add to the totals on Day 3. The   
   best upslope heavy snowfall is likely to be located across the   
   northwestward facing Adirondacks and Green Mts.   
      
   Once this system deepens across southeast Canada Sunday night into   
   Monday, very strong west-northwest flow will develop across the   
   Great Lakes and open up the potential for lake effect/upslope snow   
   into the Interior Northeast. Specifically, a multi-lake connected   
   snowband is possible extending from Lake Superior, Huron, and Erie   
   into far western NY and northwest PA given the strong northwesterly   
   flow. The latest WPC probabilities for at least 4" of snow across   
   portions of western NY and northwest PA have increased to 30-50%.   
   However locally higher amounts are possible should banding remain   
   stationary for several hours.   
      
   Snell   
      
      
   $$   
      
   = = =   
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