Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
356 PM EST Wed Nov 11 2026

Valid 00Z Thu Nov 12 2026 - 00Z Sun Nov 15 2026

...Great Lakes...
Days 1-3...

Large scale troughing will dig southward from Ontario across the
western Great Lakes and into the Midwest/Northeast, leading to
strengthening low pressure tracking from the Ohio Valley to the
Mid- Atlantic tonight into Thursday. In the wake of this system,
cold advection (850mb temperatures cooling to between -5 to -10C)
within northerly flow across the still mild lakes [Lake
temperatures +8 to +12C (Superior) and +10 to +15 (Michigan)] will
yield a delta-T of around 15-20C, supporting lake effect
precipitation. Surface temperatures will be coldest (<32F) over the
U.P. of Michigan where multi-banded snow on northerly winds will
likely accumulate several inches starting late this evening and
continuing into Saturday. The probability of at least 4 inches of
snow is >70% over the Huron Mountains (away from the warmer lake
shore) with lighter snow over much of the rest of the Upper
Peninsula and northern Lower Peninsula. Northerly flow down the
long axis of Lake Michigan could spur a robust lake band of
rain/snow into northwestern Indiana Thursday evening into Friday.
Though temperatures are marginal, the potential exists for a narrow
area of modest wet snow if rates are sufficiently high and
temperatures cool just enough. The probability of at least 4 inches
of snow is about 30-60%.


...Northeast...
Days 1-2...

The first widespread accumulating snowfall of the season is set to
arrive across the higher elevations of the interior Northeast
Thursday into Friday. Strengthening low pressure will track across
the Mid-Atlantic on Thursday before exiting the coast Thursday
night into Friday. Dynamics and forcing for ascent are impressive
with this system, aided by a potent negatively-tilted shortwave and
a dual jet structure. These features will act in tandem with
increasing warm air and moisture advection to foster increasing
precipitation from the northern Mid-Atlantic to the interior
Northeast to New England Thursday and Friday. North/northwest of
the low track, the air mass will initially be marginally cold
enough for snow or a rain/snow mix in the high elevations of the
Northeast (generally above 1500ft), mostly due to diabatic cooling
and wet-bulbing effects. As the low pressure system strengthens
further off the coast of New England, cold advection within north
to northeasterly winds will will lead to a tightening thermal
gradient and increasing low/mid-level frontogenesis. This strong
mesoscale forcing will be conducive to heavy banded precipitation,
especially within the comma-head/deformation zone. While the exact
placement of these potential bands is still somewhat uncertain,
there's risk that the increasing precipitation rates within the
bands will allow rain or rain/snow mix to change to wet snow as low
as 500ft (or less). For elevations above 1500ft, and especially
above 2500ft, a period of accumulating heavy wet snow is looking
increasingly likely, particularly Thursday night into Friday
morning. Most precipitation exits by Friday evening, though snow
showers could linger in favored upslope areas.

The probability for at least 4" of snow is 50-70% for the high
elevations of the Catskills, Adirondacks, and southern Greens, with
probabilities of 30-50% for at least 8" of snow. Given the wet and
heavy nature of snow along with many trees still having some
foliage, there's at least some risk of power outages and tree
damage. Heavy snow could also impact travel and cause slick and
snow-covered roads. As a result, WSSI-P is highlighting 40-60%
probabilities for Minor impacts and 10-20% for Moderate impacts.


...Central Appalachians...
Days 2-3...

Strong cold advection in modestly moist northwesterly flow will
lead to a prolonged period of intermittent upslope precipitation
Thursday night into Saturday. Forecast model soundings continue to
show temperature profiles through the column falling below 0C by
late Thursday night, supporting a transition from rain to snow.
Periods of light to moderate snow driven by upslope and enhanced by
weak instability will accumulate into the first half of the
weekend, especially along the spine of the central Appalachians
above 3000ft. Probabilities of at least 4 inches of snow are
20-60%, especially for the high terrain of WV and across the higher
peaks along the border of TN and NC.


...Sierra Nevada...
Days 2-3...

A strong upper wave swinging into northern CA will direct a
weakening atmospheric river into the Sierra Nevada on Friday,
leading to a quick shot of moderate to heavy upslope snow Friday
afternoon into early Saturday morning. Snow levels will initially
be around 8000ft at the start of precipitation before modestly
falling to between 6000 and 7000ft during the day on Saturday. The
heaviest snow will fall Friday evening/night when rates could
exceed 1-2"/hr. The character of the snow will likely be fairly wet
and heavy, with SLRs around 10-12:1 at best. Probabilities for at
least 8" of snow are >50% above 6500-7000ft, and for at least 12"
of snow are >50% above 7000-7500ft. Higher end scenarios for those
higher elevation bands even point to 30-50% probabilities for
accumulations of at least 24". The heavy snow will likely make for
difficult travel across some mountain passes, leading to 40-90%
probabilities for moderate impacts per the probabilistic WSSI,
mainly above 7000-8000ft.


...Northern & Central Rockies...
Day 3...

A negatively-tilted but increasingly sheared upper trough is
forecast to move across the Great Basin and Intermountain West
Friday night into Saturday. Meanwhile, ahead of the wave, a plume
of deep and anomalous moisture from a remnant atmospheric river
will overspread the region. Increasing large scale forcing for
ascent highlighted by positive differential vorticity advection and
favorable positioning in the left exit region of a 100+ kt upper
jet streak will act on this moisture and lead to widespread
precipitation production and mountain snow across the higher
elevations of the northern and central Rockies. Snow levels will
initially reside above 8000-9000ft, but will fall to between
6000-7000ft across the northern Rockies as colder air filters in
during the day on Saturday. Probabilities for snowfall
accumulations of at least 4" are >50% for the south-central
mountains in ID, from the Pine Valley mountains to the Wasatch
Plateau to the Uintas in UT, and the central mountains and San Juan
mountains in western CO. Probabilities for accumulations of at
least 8" are >50% for the Pine Valley and San Juan mountains where
moisture and forcing best overlap.


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


Miller/Fracasso