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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