Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
359 PM EST Thu Nov 6 2025

Valid 00Z Fri Nov 07 2025 - 00Z Mon Nov 10 2025

...Pacific Northwest through the Northern Rockies...
Day 1...

The last shortwave in this series which has produced consistent
active weather across the region will cross into Washington State
early D1 before translating quickly eastward into the Northern
Rockies by 00Z/Saturday. This shortwave will be accompanied by a
pronounced zonal jet streak racing across the Pacific such that
there will be a favorable overlap of height falls/PVA and left-exit
diffluence to drive significant ascent. Downstream of this
impulse, low-to-mid level southwest flow will transport copious
moisture northeast as an atmospheric river (AR) characterized by
high probabilities (>90% chance) of IVT exceeding 250 kg/m/s from
both the GEFS and ECENS ensemble systems. While this will help
produce a stripe of significant precipitation from the Pacific
Northwest through the Northern Rockies, the overall speed of the
system will somewhat limit the total amount of precipitation during
D1.

Additionally, snow levels within the core of the AR, due to the
accompanying WAA, will rise to 6000-7000 ft, but will crash behind
the associated surface cold front (and beneath the core of the
upper low) to reach as low as 3500 ft across the Cascades and into
the interior Northwest. This will allow for significant snowfall
accumulations to reach to pass level, especially at Washington and
Stevens Passes in the Cascades, where the most significant impacts
to transportation are likely.

WPC probabilities indicate a high risk (>70%) for more than 6
inches of accumulation across the northern WA Cascades, including
Washington Pass, and also extend into portions of the Northern
Rockies and in the vicinity of the Tetons.


...Northern Plains through the Great Lakes...
Days 2-3...

...Strengthening Clipper from North Dakota to Michigan...
A potent shortwave digging from Alberta, Canada will dive southeast
into the Northern Plains Friday night and then continue to
traverse rapidly southeast, reaching the Upper Midwest late
Saturday night. This feature will initially be of minimal intensity
producing modest height falls/PVA, but will steadily deepen with
time as it becomes more deeply embedded in its parent trough. By
Saturday night, the accompanying upper level jet streak will begin
to arc more poleward, producing more favorable curvature to result
in strong left-exit diffluence, which will overlap with the most
significant height falls/PVA across lower Michigan to cause
intensification of the surface low. This will occur late Saturday
night before the entire system exits into Ontario by Sunday.

While this feature will be progressive, it will likely create the
first notable snowfall of the season in a stripe arcing from North
Dakota through Iowa and into lower Michigan. Examination of
regional soundings indicates that forcing for ascent will be
somewhat modest through 00Z Sunday (end of D2) before become more
intense thanks to impressive 925-700mb fgen on WAA on D3. The DGZ
appears subjectively elevated so snow growth will be limited, but
should still accumulate lightly as reflected by WPC probabilities
for 1+ inches of 10-50% aligned from central ND through northern
IA. Although this snowfall is not exceptional, it will be impactful
as it likely to be the first accumulating snowfall of the season
for this region.

During D3, however, forcing intensifies, especially across lower
Michigan where mesoscale analysis indicates a moderate threat for
CSI due to impressive fgen overlapping the DGZ and driving ascent
into a region of theta-e lapse rates of 0C/km. The SREF 3-hr
snowfall probabilities indicate the potential for 2-3" during this
time, and 1"/hr snowfall appears reasonable during this period of
most intense lift. Despite the rapid progression of the wave, this
could result in more than 4 inches of snow, especially across lower
Michigan in the vicinity of Detroit, where WPC probabilities for
more than 4 inches of snow reach 10-30%.

...Lake Effect Snow beginning Sunday...

A strong vort max digging southward from Ontario, Canada into the
Great Lakes will help carve out a deepening and amplifying
mid/upper level trough across much of the eastern U.S. starting on
Sunday. Strong CAA underneath this vort max/trough and in the wake
of a strengthening surface low tracking northeast into
Ontario/Quebec will deliver a notably colder, winter-like air mass
to the region, headlined by 850mb temperatures between 10 and 15
degrees below 0C. This injection of unseasonably cold air (near or
below the 10th climatological percentile) over top the warm Great
Lakes (temperatures of +10 to +15C) will result in an impressive
convective environment with model soundings revealing steep lapse
rates and deep mixing heights to near or above 700mb. Given delta
Ts of 20 to 30C, the environment appears more than supportive of
lake effect snow production.

Lake parallel north-northwest to northerly surface winds along
with increasingly unidirectional winds aloft will act on the
impressive instability highlighted above. Combined, this will
support the development of a few prominent north-south lake effect
snow bands, particularly downwind of Lake Superior and Lake
Michigan during the D3/Sunday period. These snow bands will
primarily be focused across portions of the U.P of Michigan, where
the heaviest snowfall may exceed (50% chance) 4 inches. Additional
lake effect snowfall is expected along and just inland of the
eastern lake shore of Lake Michigan, and across northern Indiana,
where WPC probabilities for 2+ inches are as high as 30%.
Additionally heavy lake effect snow is expected beyond this
forecast period into D4 as well.


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


Weiss/Miller