Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
148 AM EST Sat Nov 14 2026

Valid 12Z Sat Nov 14 2026 - 12Z Tue Nov 17 2026


...Northeast...
Day 1...

Impressive mid-level trough across the eastern CONUS will meander
through Saturday as the core (closed low) drops across Maine while
slowly opening. Height anomalies across the east are progged to
drop below the 2.5th percentile, indicative of the anomalous nature
of the trough. At the same time, as the upper low center drops
across Maine, it will shed a vorticity lobe southeast from Upstate
NY through the Mid-Atlantic, beneath which a surface trough will
dig southeast as well. Together, this evolution will enhance the
ongoing cold air advection (CAA), increase lapse rates to drive
strong instability, and cause enhanced ascent through upslope flow,
especially in the upwind Adirondacks and Greens. Additionally, lake
enhanced moisture from the eastern Great Lakes will spread
southeast - the result of which will be an expansion of SE
advancing precipitation in streamers or convective rain/snow
showers.

The heaviest accumulations are likely in the upwind terrain of the
Adirondacks and the Greens where the probability of at least 4" is
as high as 30-50%, with local 4" snowfall also possible across the
higher terrain of the Whites in NH. Elsewhere, while amounts will
be less, streamers and convective snow showers with brief gusty
winds and heavy rates to cause difficult travel will occur across
much of northern PA, Upstate NY and into parts of northern/central
New England.


...Western United States...
Days 1-3...

Two distinct troughs and accompanying atmospheric rivers (ARs) will
continue an active pattern with high-elevation snow across much of
the West through mid-week.

The first trough will be exiting the Great Basin and pushing east
into the Central High Plains as a positively tilted feature today
into tonight. An overlap of mid-level height falls with modest jet
diffluence occurring immediately downstream of a surface cold front
will provide deep layer ascent into the still moist column. This
deep layer lift combined with locally enhanced ascent through
upslope flow will result in periods of heavy snow today and
tonight, especially across the Wasatch, Uintas, San Juans, and
Sangre de Cristos. Snow levels are expected to be elevated at
7000-9000 ft, but above these levels there is a high chance
(50-80%) of at least 6" of snow, with locally as much as 12" in the
San Juans.

As this feature ejects eastward late D1 into D2, a more substantial
trough develops off the Pacific Coast stemming from a closed low in
the Gulf of Alaska. A lobe of vorticity shedding from this primary
low will advect towards the OR/CA coast by Monday morning, with the
downstream AR providing IVT above 500 kg/m/s with a S/SW direction
impinging onshore. This will occur ahead of a subsequent cold
front, and the accompanying warm air advection (WAA) will surge
snow levels to support heavy snow above around 8000 ft, before
crashing in the wake of the cold front to as low as 4500 ft. This
will support snowfall rates of at least 1"/hr late Sunday into
Monday across the Sierra, northern CA ranges, and parts of the
Cascades, supporting a high probabilities (>70%) for at least 6"
accumulation despite the limited temporal duration of heavy snow.

As the front shifts into the Great Basin and Northern Rockies into
D3, intensifying fgen is likely to develop in response to both the
low-level baroclinic gradient, but also enhancement from the
poleward arcing jet streak downstream of the primary trough axis.
While there is still a bit of uncertainty as to the timing of this
front, the impressive lift along it combined with rapidly cooling
snow levels will support an arc of heavy snowfall from the Sierra
northeast across much of central/northern NV and into the mountains
and even elevated valleys of ID and western MT which will produce
difficult travel across these areas.

The probability of significant ice across the CONUS is less than
10 percent.


Weiss