Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
349 AM EDT Tue Mar 31 2026

Valid 12Z Tue Mar 31 2026 - 12Z Fri Apr 03 2026

...Potentially impactful mixed precipitation event increasingly
likely for the Upper Midwest into the Great Lakes Thursday...


...Sierra Nevada to the Rockies...
Days 1-2...

An incoming shortwave out of the Pacific this afternoon will bring
some light to perhaps modest snow to the Sierra Nevada, Wasatch,
Uintas, and CO Rockies as it zips eastward. To the north, lingering
moisture along a stationary surface boundary will maintain light
snow over the ID ranges into Wyoming with additional accumulation.
Snow levels will be high (8000-9000ft to the south, though falling
~1000ft as the trough moves through) with WPC probabilities for at
least 8 inches of snow are at least 50% above 7500ft (Sierra) to
10,000ft (CO). Totals in the CO Rockies may eclipses a foot above
11,000ft. Over ID into WY, WPC probabilities for at least 8 inches
of snow are at least 50% above 8000ft.


...Pacific Northwest to the Northern Rockies...
Days 2-3...

A powerful closed upper-low diving southward from the Gulf of
Alaska will be the catalyst for renewed mountain snow in the
Olympics, Cascades, the Salmon/Siskiyou of northern CA, and as far
east as the Blue Mountains Wednesday afternoon and continuing
through Thursday. The approaching 850-500mb layer heights
associated with the closed low are below the 10th percentile and
snow levels will be able to drop as low as 2,000ft Wednesday night
in the Olympics, Cascades, and even as far south as the Siskiyou. A
steady stream of Pacific moisture embedded within SWrly mean layer
flow, suitable for upslope enhancement as well, will also favor
locally heavy snowfall rates in these ranges. Drier air should move
in on the backside of the closed low by Thursday afternoon,
although lingering westerly low-level winds should support light-
to-moderate snow in the Cascades for the remainder of the day on
Thursday with all precipitation ending by early Friday morning west
of the Divide.

To the east, snow will start overnight tomorrow night and continue
through this forecast period (12Z Fri) over Montana. With a closed
low track from the WA/OR border ESE across central ID into central
WY, snow will maximize over the Blue Mountains, Bitterroots,
Absarokas, Tetons and into the Bighorns. The western MT ranges will
also see moderate snow totals closer to the 700mb low and old
triple point surface low.

WPC 48-hour probabilities for at least 12 inches of snow are high
(>70%) in the OR Cascades above 4,000ft with at least moderate
chances (>50%) for snowfall totals >8" at elevations >3,000ft. The
WA Cascades will see lesser snowfall totals than their OR neighbors
given the best Pacific moisture plume will reside farther south,
but several inches of snow at pass level (Snoqualmie and Stevens)
are expected. To the east, WPC probabilities for at least 12 inches
of snow are at least 50% above 7000ft or so.


...Northern New York and New England...
Days 1&3...

A lingering front will become the focus for organized
precipitation as a series of low-amplitude southern stream waves
interact with deepening moisture. Light precipitation will spread
across the region today with the first wave, followed by heavier
precipitation tonight as a following wave strengthens ahead of a
more amplified northern stream wave moving across Quebec. While
southwesterly flow aloft advects warmer air into the mid-levels, a
shallow but stubborn layer of sub-freezing air is expected to
remain entrenched across northern New England. Forecast soundings
support mostly snow across far northern Maine, while areas farther
south, including areas as far south as Downeast Maine, may see snow
transitioning to accumulating ice. Guidance continues to indicate
that northwestern Maine is the area mostly likely to be impacted
with heavier ice accumulations. WPC probabilities of at least a
tenth of an inch of ice are 30-50% over the Central Highlands and
northern White Mountains. Northern Aroostook County has the highest
chance of staying all snow, with WPC probabilities of at least 4
inches 50-90%.

Following a brief dry period Wednesday night, the threat for
wintry weather is forecast to return to the region on Thursday as
the system detailed below lifts toward the Great Lakes -- bringing
moisture back into the region as cold high pressure remains
anchored to the north. For Day 3, the setup again would favor all
snow over far northern Maine then quickly transitioning to sleet
and freezing rain for the Central Highlands southwestward through
much of northern NH, the Northeast Kingdom of Vermont, and the
northern Adirondacks. WPC probabilities for at least 4 inches of
snow are 30-50% along the northern Maine border with Canada (North
Woods area). For freezing rain, WPC probabilities for at least a
tenth of an inch of ice are at least 30% over the northern CT River
Valley/Northeast Kingdom into central/northern NH and northwestern
Maine.


...Upper Midwest/Corn Belt/Western Great Lakes...
Days 2-3...

An amplified shortwave exiting the Rockies Wednesday night will
lift toward the Great Lakes, directing a deep plume of Gulf
moisture to the north. As precipitation blossoms across the region
on Thursday, a sharp thermal gradient north of the I-80 corridor
will support a broad swath of wintry weather, topped by a west-
east band of heavy snow and bordered to the south by a corridor of
sleet and freezing rain, with significant ice accumulations
possible. Uncertainty remains high overall due to a shifting storm
track in the models (northwest trend since yesterday) and ptype
uncertainty through the storm evolution as many areas will see a
transition from snow or sleet to freezing rain and perhaps just
rain. Though precipitation may be still ongoing at the end of this
forecast period (12Z Fri), the heaviest will likely be on Thursday.

Through 12Z Friday, WPC probabilities for at least 4 inches of
snow are at least 50 percent from portions of the eastern Dakotas
through much of central to northeastern MN (especially the
Arrowhead), northern WI, and into the western U.P. of Michigan. The
highest probabilities of snowfall in excess of 8 inches lies over
the Arrowhead (30-60% chance).

The freezing rain may be significant within a broad region that
may see at least some icing; namely, SD through MN and WI to MI.
WPC probabilities for at least a tenth of an inch of ice are at
least 30% over much of Wisconsin into the U.P. and the northern 1/3
of Lower Michigan. Some areas could see in excess of 0.25" icing,
specifically central WI and northern Lower Michigan, but this is
subject to change with the storm track. The probability of Moderate
impacts per the WSSI-P are at least 40% in these areas.


Fracasso/Mullinax/Pereira