Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
406 PM EST Fri Nov 7 2025

Valid 00Z Sat Nov 08 2025 - 00Z Tue Nov 11 2025

...Northern Plains through the Interior Northeast...
Days 1-3...

...Strengthening low from North Dakota to the Northeast...
A potent shortwave pivots southeast from eastern Montana
this evening and digs to Iowa through Saturday, producing the first
accumulating snow of the season for some locations in the Midwest
and Great Lakes. A reinforcing trough then dives south over the
Upper Midwest Saturday night before developing into a deep low over
the Great Lakes Sunday night. The surface low rapidly develops
over the eastern Great Lakes Saturday night downstream of the
reinforcing trough and mainly tracks along/north of the St.
Lawrence in eastern Canada Sunday.

While this feature is progressive over the northern Plains, it
will create a stripe of snowfall on the northern/northwestern
periphery of the low pressure system. This includes a swath from
ND (where Day 1 NBM snow probabilities for >2" are around 25%)
with lesser amounts over eastern SD, down through IA, the WI/IL
border region and further into the Lower Great Lakes. However,
forcing intensifies by the time it reaches IA and as it crosses
into the Lower Great Lakes Saturday afternoon and evening 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
Saturday night. This may lead to snowfall rates exceeding
0.5-1.0"/hr at times, as depicted by the HREF snowband probability
tracker. Day 2 NBM snow probabilities for >2" are 20-30% over
central lower Michigan.


...Lake Effect Snow beginning Sunday...
The deepening and amplifying mid/upper level trough over the
central Great Lakes Sunday that develops into a deep low Sunday
night will bring Strong CAA and a winter-like air mass to the
region, headlined by 850mb temperatures between negative 10 and 15
degrees C. 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 lake
temp and 850mb air temp delta Ts of 20 to 30C, the environment
appears more than supportive of lake effect/enhanced snow
production.

North-northwest to northerly surface winds along with increasingly
unidirectional winds aloft will act on the instability and support
the development of a few prominent north-south lake effect snow
bands, particularly downwind of Lake Superior Sunday and Lake
Michigan Sunday night into Monday. Day 2 NBM probabilities for >4"
are 40-80% across portions of the U.P. of Michigan and the far NW
corner of lower Michigan. There is increasing confidence for
enhanced banded snow aided by a potent vort max and a potential
lake induced mesolow Sunday night into Monday morning over parts
of northeast Illinois (including the Chicago metro) and northern
Indiana. Day 3 NBM probabilities for >4" are 40-80% with
probabilities for >6" 30-70%. This area, along with downstream
snow banding from Lake Erie will need to continue to be monitored
for the heavy snow banding threat given the potential for early
season impacts.

Cold upslope northwesterly flow will also lead to increasing snow
potential across parts of the Appalachians on Day 3/Monday, with
NBM probabilities highlighting probabilities for >4" of 25-50%.


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


Snell/Miller