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   FOUS11 KWBC 152025   
   QPFHSD   
      
   Probabilistic Heavy Snow and Icing Discussion   
   NWS Weather Prediction Center College Park MD   
   325 PM EST Sat Nov 15 2025   
      
   Valid 00Z Sun Nov 16 2025 - 00Z Wed Nov 19 2025   
      
   ...Upstate New York and New England...   
   Days 1-3...   
      
   Broad but persistent troughing across the east will be re-energized   
   by a potent shortwave digging southeast from Ontario into Northern   
   New England Sunday. This shortwave is likely to amplify as it   
   progresses southeast, becoming a closed low over Maine Sunday night   
   before exiting into the Canadian Maritimes. The accompanying polar   
   jet streak will rotate around this trough, placing favorable LFQ   
   diffluence overlapping the strongest height falls, and the result   
   of this will be a deepening surface low tracking across Northern   
   New England, with both the accompanying WAA and CAA leading to   
   widespread wintry precipitation through early next week.   
      
   Precipitation will expand across Upstate NY and then spread into   
   New England early D1 /00Z Sunday/ in response to increasing 850mb   
   WAA and the accompanying omega driven by fgen. As this occurs, the   
   surface high pressure in place will retreat gradually, allowing for   
   the strong WAA to overwhelm the cold air in place. At this time,   
   the regional soundings suggest limited to no dry-air replacement (a   
   lack of E/NE low-level flow) to maintain wet-bulb temps below 0C.   
   This suggests that eventually this WAA will overwhelm the column,   
   turning precipitation to all rain most areas outside of the highest   
   Presidential peaks and parts of northern/central ME. As 850mb temps   
   climb, this suggests that precip will begin as snow/sleet/freezing   
   rain, before transitioning. Where the initial p-type is snow, a   
   burst of snow is likely (northern NH and ME), and snowfall rates   
   may reach 1"/hr at times, although a relatively shallow and   
   modestly-saturated DGZ will limit more intense snowfall. Across   
   other parts of the higher elevations of NY/VT/NH, a period of   
   freezing rain is likely, with moderate accretions expected by   
   Sunday morning. WPC probabilities for freezing rain have increased,   
   and now reach as high as 50-70% for 0.1+" across the high terrain   
   of the Adirondacks, Greens, and Whites, with locally more than   
   0.25" possible (10-30% chance) near the Presidential Range.   
      
   The forecast then gets even more challenging as the surface low   
   races eastward while deepening, leading to enhanced moisture   
   transport and a modest TROWAL pivoting across ME, while robust CAA   
   helps drive an extended period of upslope snowfall as well.   
      
   Across Maine, beginning late D1 through the first half of D2, the   
   CAA behind the low will combine with isallobaric flow to rapidly   
   cool the column, changing precipitation to all snow. At the same   
   time, increasing moisture within the TROWAL and some developing   
   deformation on the back side of the 700mb wave will lead to an   
   expansion of snowfall potentially down to the coast as the dry slot   
   moistens, and periods of moderate to heavy snowfall are possible   
   in response to an inverted trough pivoting southeast. There is a   
   lot of uncertainty among the available high-res models, but at   
   least some modest snowfall is possible through D2 all the way to   
   the coast.   
      
   A higher-confidence threat for heavy snow develops on the windward   
   side of the terrain of the Adirondacks, Greens, and Whites through   
   D2 as strengthening CAA on accompanying NW flow moves into the   
   area. Initially, the DGZ appears dry so a period of freezing   
   drizzle or light freezing rain is expected in the higher terrain   
   once again (adding to ice which accreted earlier D1). However, this   
   should quickly saturate during Sunday coincident with a rapid   
   deepening of the DGZ. With impressive ascent driven by the upslope,   
   and Froude numbers progged to be around 1.25, an extended period of   
   heavy snow is likely across the upwind terrain and across the   
   crests, although downwind snowfall should be much lighter. The   
   guidance continues to trend upward during this period. For D1 and   
   D2, WPC probabilities suggest a moderate risk (~50% chance) for 4+   
   inches on both days in the Adirondacks, Greens, and Whites, with a   
   high chance across Northern ME. Locally, 2-day snowfall of 8-12"   
   is probable in parts of ME (where precipitation stays all snow) as   
   well as the higher terrain elsewhere due to the prolonged upslope,   
   leading to a moderate impacts across these areas. Closer to the   
   coast, especially in ME, confidence is much lower, but WPC   
   probabilities do indicate a moderate threat (30-50%) for at least   
   2" of snow across the eastern half of the state.   
      
   By D3, NW flow begins to ease, but lingering upslope snowfall,   
   especially across the Adirondacks, Greens, and Whites, will   
   continue in a more limited fashion through the day, with additional   
   modest accumulations likely.   
      
      
   ...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 closed upper low is forecast to swing inland Saturday night   
   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 will allow for gradually falling snow levels, ample lift,   
   and widespread moderate precipitation. As the associated moisture   
   plume moves inland across the Intermountain West through Sunday   
   night, moderate to locally heavy snow is likely for much of the   
   central and northern Rockies, with the highest totals for the San   
   Juan, southern Wasatch, and Uinta Mountains where up to a foot of   
   snow accumulation will be possible.   
      
   Snow levels will once again start out above 9k feet across much of   
   California, 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.   
      
      
   ...Great Lakes...   
   Days 1-3...   
      
   Once the low pressure 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 are generally about 30-50%. However locally higher amounts are   
   possible should banding remain stationary for several hours.   
      
   The potent upper level low currently situated near southern   
   California is progged to move inland and cross the central Plains   
   going into Monday, while evolving into an open wave. This will   
   sustain a modest low pressure system tracking from Kansas to   
   southern Indiana by late Tuesday. Isentropic ascent well to the   
   north of the attendant cold front will likely result in a broad   
   area of mainly light to moderate precipitation extending as far   
   north as southern Wisconsin and southern Michigan. Model forecast   
   soundings indicate there may be enough low level cold air present   
   to support a period of light snow, or a mix of rain and snow at the   
   onset, and mainly rain south of the Indiana/Michigan border. This   
   currently does not appear to be an impactful event with most   
   snowfall amounts generally under an inch.   
      
   Weiss/Hamrick/Snell   
      
      
   $$   
      
   = = =   
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