Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
300 PM EDT Mon Mar 30 2026

Valid 00Z Tue Mar 31 2026 - 00Z Fri Apr 03 2026

...Northern Rockies...
Days 1-3...

A cold front pushing south and east through the northern Rockies
today will work together with an influx of 700-300mb layer moisture
and the diffluent right-entrance region of a 250mb jet streak to
produce snow from the Bitterroots on east through the Absaroka,
Wind River, Teton, and Big Horn Ranges tonight and into Tuesday.
Snow ill linger through Tuesday due to weak upslope easterly flow
from high pressure over southern Saskatchewan and and moist SWrly
700mb winds maintaining a steady fetch of Pacific moisture.
Snowfall rates will generally be on the light side on Tuesday with
weakening synoptic-scale lift aloft. Through 00Z Wednesday, WPC
probabilities depict moderate-to-high chances (50-80%) for snowfall
totals >4" in the Absaroka, Tetons, Wind River, and Big Horn
ranges. The peaks of the MT/WY Absaroka and the Wind River
mountains may witness some localized snowfall totals approaching a
foot.

Periods of light mountain snow will continue through Tuesday night
and Wednesday morning before the next round of heavier mount snow
arrives Wednesday night. The 500mb low responsible for the heavy
mountain snow in the Pacific NW will direct its rich plume of
Pacific moisture into the Northern Rockies. At the same time, its
diffluent 250mb left-exit quadrant will be in place over the
region at the same time healthy 500mb PVA occurs. There is no
frigid air-mass in advance of this system, keeping most heavy
snowfall above 4,000ft from the Bitterroots and Sawtooth on east to
the Lewis Range. For the Absaroka, Tetons, and as far east as the
Big Horns, heavier snowfall totals will be at/above 7,000ft. WPC
probabilities highlight at least moderate chances (>50%) for
snowfall totals >6" in the peaks of all these aforementioned ranges
with localized totals up to a foot possible. The WSSI-P shows that
there are high chances (>70%) for Minor Impacts in the peaks and
passes of these regions, but Moderate Impact probabilities remain
on the low side (<20%). This indicates some hazardous travel is
possible, although more significant impacts are not anticipated at
this time.

Many of these mountains regions are either right around normal, or
below normal for the season-to-date snowfall, so snowfall in the
northern Rockies will be more beneficial than harmful as we
approach the start of the warm season.


...Pacific Northwest...
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 closer 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.

WPC 48-hour probabilities show high chances (>70%) for snowfall
totals >12" 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. The peaks of the Siskiyou
and Salmon Mountains of northern CA, as well as the peaks of the
Blue Mountains of northeast OR, all have high chances (>70%) for
snowfall totals surpassing 8". Most impacts on the WSSI currently
show Minor Impacts with locally Moderate Impacts depicted in the
peaks of these mountain ranges through Thursday.


...Sierra Nevada to the Colorado Rockies...
Days 2-3...

An incoming shortwave out of the Pacific Tuesday afternoon will
bring some light to perhaps modest snow to the Sierra Nevada,
Wasatch, Uintas, and CO Rockies as it zips eastward. Snow levels
will be high (8000-9000ft 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.


...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 on Tuesday with the first wave, followed by
heavier precipitation Tuesday night 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 subfreezing
air is expected to remain entrenched across northern New England.
Forecast soundings support mostly snow across far northern Maine,
while areas further south, including areas as far south as Down
East Maine may see snow transitioning to accumulating ice. The
latest guidance indicates that northwestern Maine is the area
mostly likely to be impacted with heavier ice accumulations, with
WPC probabilities showing 30-50 probabilities for ice accumulations
of 0.10 inch or more centered across the region 00Z Wednesday -
00Z Thursday. Northern Aroostook County is likely to be the focus
for the heaviest snow accumulations, with WPC probabilities
indicating that amounts greater than 4 inches are likely (50-70
percent).

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 the 24-hr period ending 00Z Friday, WPC
probabilities indicate that additional accumulating ice is likely
for parts of the Adirondacks, with lower probabilities extending
east to Down East Maine.

...Upper Midwest/Corn Belt/Western Great Lakes...
Day 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 west-east
band of heavy snow and bordered to the south by a corridor of
sleet and freezing rain, with significant ice accumulations
possible.

Through 00Z Friday, WPC probabilities greater than 50 percent for
snow accumulations greater than 4 inches are largely confined to
the Minnesota Arrowhead eastward to the western U.P.

At this point, guidance indicates that significant icing will be a
more far-reachiing concern. By 00Z Friday, the P-WSSI shows
probabilities greater than 50 percent for moderate impacts due to
icing continuing to expand across the region, now covering parts
of southeastern Minnesota and northeastern Iowa, as well as large
potions of central and southern Wisconsin, and northern and central
Lower Michigan. For the 24-hr period ending 00Z Friday, WPC
probabilities for ice accumulations greater than 0.10 inch are
50-70+ percent across this area, with the higher probabilities
generally corresponding with 30-50 probabilities for ice
accumulations greater than 0.25 inch.

Mullinax/Pereira/Fracasso