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

Valid 00Z Wed Apr 01 2026 - 00Z Sat Apr 04 2026


...Northern Plains through the Great Lakes...
Days 1-3...

...Significant late season snow and freezing rain likely to create
substantial impacts through mid-week...

Late season winter storm will begin on Wednesday as a lee side low
pressure system develops across eastern Colorado. This low will
develop in response to a shortwave which will emerge from the
Pacific over California and then sharpen as it moves across the
Four Corners Wednesday. This shortwave is expected to then develop
a negative tilt as it pushes into the Upper Midwest Thursday before
exiting into Canada by Friday morning. The combination of
impressive downstream divergence ahead of this sharpening
shortwave, followed by height falls and the LFQ of a modest but
strengthening meridionally arcing jet streak will provide
widespread deep layer ascent to help deepen the surface low as it
tracks from Colorado northeast into Michigan.

The challenge for this period primarily revolves around the track
and timing of this low, as there is high confidence in its
development. Over the past 4 cycles of the ECENS and GEFS, the
surface low clusters have become more consolidated, but continue to
feature a subtle N/NW trend. This is in response to a small
deepening trend in the upper pattern, although the EC-AIFS has been
exceptionally consistent with its track, so while the NW trend may
continue, it appears that is slowing and beginning to consolidate
leading to higher confidence overall.

As this low develops and tracks northeast, impressive moisture will
spread northward to support a large swath of all p-types. An
impressive IVT plume (>90% for 250 kg/m/s pushing well into the
Rockies) will support upper level moisture into the system, while
low-level moisture fueled by increasing WAA out of the Gulf help to
saturate the low-levels. The accompanying theta-e ridge emerging
northward will help expand the precipitation shield thanks to PW
anomalies that surge above the 99th percentile according to NAEFS.
This will result in periods of heavy precipitation, first across
the Dakotas Wednesday morning and then expanding eastward within
the WAA plume, reaching Michigan by Thursday morning, with
precipitation continuing through Thursday night, potentially
Friday morning across northern MN, before ending across the area.

In the locations that receive mostly snow, which is expected to be
the Dakotas, and the northern half of Minnesota, heavy
accumulations appear likely. In this area, snowfall rates of 1"/hr
appear likely through both WAA and then deformation on the NW side
of the low as it deepens, leading to 48-hr WPC probabilities that
are moderate (50-70%) for at least 4 inches of snow, with locally
more than 8 inches possible (10-30%) from the Buffalo Ridge through
the Arrowhead of MN and the western U.P. of MI. Lighter snowfall of
2-4" is likely south/east of this axis including the northern
suburbs of the Twin-Cities and Green Bay, where heavy snow will
develop but rapidly changeover to a mix and then rain, leading to
lesser snowfall.

The most substantial impacts from this event may be due to freezing
rain rather than ice. Although the Canadian high pressure over
Ontario will retreat quickly, antecedent wet-bulb temperatures are
well below freezing (in the low to mid 20s) due to very dry
dew point temperatures. Although these will slowly warm as the
impressive warm nose surges northward, there is likely to be an
extended period of freezing rain (after a period of snow and sleet)
from the IA/MN border northeast through much of WI and into the
northern L.P./eastern U.P. of MI. Exceptional WAA within the warm
nose, anomalous column moisture, and a lack of strong dry advection
to offset the latent heat release of freezing should limit the
freezing rain accretion efficiency. However, there is still likely
to be a long duration of freezing rain leading to significant and
impactful icing for which WPC probabilities indicate at least a 70%
chance of 0.1", with a 40-60% chance for at least 0.25" across WI.
Locally, more than 0.5" is possible (10-30% chance) in central WI
but at this time that appears to be more the exception than the
rule. Regardless, considerable impacts from icing are likely as
reflected by the WSSI-P which indicates a 60-80% chance for
moderate impacts.

Key Messages for this winter storm have been initiated. A link to
view the Key Messages are below.


...Sierra Nevada to the Central Rockies...
Days 1-3...

A shortwave trough is beginning to track into CA today and will
race east through the Great Basin tonight and over the central
Rockies by Wednesday. An impressive plume of Pacific moisture
(NAEFS shows IVT values of at least 99.5 climatological percentile
over the Southwest) will be directed at the Central Rockies with
periods of heavy mountain snow from the Wasatch on east through the
CO Rockies. Snow will be at its heaviest over the CO Rockies and
Wasatch tonight with lingering heavy snowfall continuing into
Wednesday. Snow rates will decrease by Wednesday night but some
lingering light mountain snow will continue. WPC probabilities show
high chances (>70%) for additional snowfall >6" in the central and
southern Sierra Nevada through Wednesday. The heaviest snowfall in
the Wasatch will occur above 8,000ft where as much as 6-12" of
snowfall is expected. The snowfall "jackpot" is in the CO Rockies
at/above 9,000ft where snowfall is likely to surpass 12" and may
approach 20" locally.

There is not much of a break in the snowfall as the next closed low
tracking through the Northwest directs yet another anomalous IVT
(200-300 kg/m/s, or above the 90th climatological percentile per
NAEFS) at CA and the Great Basin on Wednesday. Snow levels in the
northern CA ranges (Trinity, Siskiyou, Salmon) drop to as low as
3,000ft) with minor accumulations down to 3,000ft while heavier
totals (amounts surpassing 6") will generally be found at/above
5,000ft. Farther south, the northern Sierra Nevada above 6,000ft
have moderate-to-high chances (50-80%) for snowfall totals >6"
through Wednesday night. This same moisture source works its way
across the Wasatch, Uinta, and Bear River Ranges of UT, including
the southern WY and northern CO ranges by Thursday and lingering
through early Friday. WPC probabilities show moderate-to-high
chances (50-80%) for additional snowfall >8" in the listed UT
ranges with similar probabilities in the Park and Medicine Bow
ranges of WY/CO.

In summary, any significant impacts will be confined to the higher
elevations of these ranges, with one exception being I-80 and
US-50 over
the Sierra Nevada where the the WSSI shows Moderate Impact
potential. Most of these mountain ranges east of the Sierra Nevada
are well below normal for cold season snowfall, so while some
travel impacts are possible, the snowfall is also welcomed with
the cold season now well into its "fourth quarter", so to speak.


...Pacific Northwest to the Northern Rockies...
Days 1-3...

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 2.5 percentile per
NAEFS and snow levels will 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 on the
backside of the closed low arrives 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. Precipitation tapers off east of the Divide by Thursday
night.

Farther east, snow will start Wednesday night and continue through
this forecast period (12Z Fri) over Montana. The closed low will
weaken to an extent, but it remains well intact as it moves east
with healthy upper-level divergence out ahead of the closed low.
In addition, NAEFS shows >90th climatological percentile levels
for 500mb and 700mb mean specific humidity (g/kg), indicating
unusually high moisture content higher up in the atmospheric
column. With a 500mb low track from the WA/OR border ESE across
central ID into central WY, snow will be heaviest on the low's
northern flank across 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 added assist of
low-level easterly flow that results in upslope enhancement.

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 moderate-to-high (50-70%) above 7000ft or so. The peaks
of the Blue, Sawtooth, Absaroka, and Tetons have low-to-moderate
odds (30-50%) for snowfall totals topping 18" through Friday.


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

A pair of sheared 500mb vorticity maxima tracking through northern
New England will be accompanied by a steady stream of 850-300mb
moisture aloft to produce periods of snow over far northern Maine
and a wintry mix of sleet/freezing rain in central Maine today and
tonight. As a wave of low pressure tracks along a warm front
draped over northern New England tonight, additional wintry
precipitation will develop and produce additional snow and ice
accumulations through Wednesday morning. WPC probabilities show at
least moderate chances (>50%) for additional snowfall totals over
4", while central Maine sports at least moderate chances (>50%) for
additional ice accumulations over one-tenth of an inch.

Following a break in the snow and ice Wednesday afternoon and
through much of the day on Thursday,moisture streaming north out
ahead of the Midwest winter storm will be paired with increasing
850-700mb WAA aloft that produces more precipitation. High pressure
over Quebec will help to lock in sub-freezign wet-bulb temps from
the White Mountains on north through interior Maine, allowing for
yet another round of wintry precipitation Thursday afternoon and
lingering through Thursday night. Snow will be the primary
precipitation at the onset in northern Maine, but even northern
Maine will flip over to a wintry mix Thursday night and continue to
contend with freezing rain into Friday morning. Eventually, strong
low-level WAA will erode the sub-freezing temperatures at the
surface and precipitation will changeover to plain rain. Prior to
the changeover to rain, WPC probabilities show low-to-moderate
chances (30-50%) for ice accumulations over one-tenth of an inch
over the White Mountains and along the Maine/Quebec border. Similar
 are present for >4" of snowfall over far northern Maine through
Friday morning.

...Northern Plains...
Day 3...

No rest for the weary in the Northern Plains, as the departure of
one winter storm only means the arrival of yet another storm system
on Friday. A slow moving 500mb closed low over WY will generate
healthy PVA aloft and increased 700mb Q-vector convergence over the
northern High Plains. Snow will already be falling over central MT
and the Big Horns Thursday night, but as a surface low strengthens
along the KS/NE border Friday morning, 850-700mb WAA to the north
of the low will support banded precipitation on the northern flank
of the 500mb low. Guidance is in good agreement on the presence of
a very moist 700-300mb column, although exact placement of the
heaviest QPF axis is still unclear. Still, hazard-focused guidance
such as the ECMWF-EFI is showing a signal up to 0.8 for QPF from
the MT/WY border on east to SD. This product shows the potential
for an unusual amount of QPF at this storm's disposal, with thermal
profiles that do support snow on the storm's northern and western
flanks.

WPC probabilities show a large swath of at least moderate-chance
probabilities (>50%) for >4" of snow from northeast WY and southern
MT through northern SD and southern ND. Given the slow progression
of the upper low and likely banding associated with this storm,
snowfall rates >1"/hr for prolonged windows could result in
localized amounts exceeding 12". This is evident in WPC
probabilities that show low chances for >12" totals in northwest SD
and southwest ND. Lastly, there is the potential for some icing
closer to the warm front farther east. WPC probabilities show low-
to-moderate chances (30-50%) for ice accumulations over one-tenth
of an inch in southeast SD and southwest MN. Residents in the
Northern Plains should continue to monitor the forecast closely as
any subtle change in track or change in the storm's intensity could
mean notable changes to expected snowfall totals.


Mullinax/Weiss



...Winter Storm Key Messages are in effect. Please see current
 Key Messages below...

https://www.wpc.ncep.noaa.gov/key_messages/LatestKeyMessage_1.png