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