Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
426 AM EDT Wed Apr 1 2026

Valid 12Z Wed Apr 01 2026 - 12Z Sat Apr 04 2026


...Northern Plains through the Great Lakes...
Days 1-2...

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

Late-season winter storm will begin tonight as an exiting
shortwave out of the Rockies spurs a lee-side low pressure system
this afternoon. 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 strengthen the surface low as it tracks from
Colorado northeastward into Michigan.

Impressive moisture will spread northward to support a large swath
of all p-types that move through time during the event. Ample
upper-level moisture from the southwest and low-level moisture
fueled by increasing WAA out of the Gulf will 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 this
morning and then expanding eastward within the WAA plume, reaching
Michigan by Thursday morning. Precipitation will continue through
Thursday night and eventually end from southwest to northeast on
Friday morning.

In the locations that receive mostly snow, which is expected to be
mostly in the northern half of Minnesota, modest to locally heavy
accumulations appear likely. In this area, snowfall rates of 1"/hr
are likely via deformation on the NW side of the low as it deepens,
leading to 48-hr WPC probabilities that are moderate/high (50-80%)
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 (40-60%) and into the Keweenaw Peninsula. Lighter snowfall of
2-4" is likely south/east of this axis north of the Twin-Cities and
Green Bay. In these regions, heavy snow will develop but rapidly
change over to a wintry mix and then rain, leading to lesser
snowfall.

The most substantial impacts from this event may be due to
freezing rain. Although the Canadian high pressure over Ontario
will retreat quickly, antecedent wet-bulb temperatures are well
below freezing (in the low to mid 20s this morning) 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 eastern SD and along/north of the IA/MN border 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
40-70% chance for at least 0.25" across WI. Locally, more than 0.5"
is possible (10-40% chance) in central WI. Considerable impacts
from icing are likely as reflected by the WSSI that shows
widespread moderate to locally major impacts.

Please see a link to view the Key Messages at the end of this
discussion.



...CA/Great Basin to the Central Rockies...
Days 1-2...

A shortwave trough over the Great Basin this morning will continue
eastward today. 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 wane from west to east today over NV/UT but
continue over the CO Rockies through the day and diminishing
overnight. WPC probabilities for an additional 6 inches of snow are
>50% over the Wasatch and Uintas. Over the CO Rockies, WPC
probabilities for at least an additional 12 inches of snow are >50%
above 10,000ft.

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 starting later today. Snow
levels in the northern CA ranges (Trinity, Siskiyou, Salmon) drop
to as low as 3,000ft with minor accumulations. 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
tomorrow morning. 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 trying to make up for lost time.


...Pacific Northwest to the Northern Rockies...
Days 1-2...

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 this 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 tonight and continue through Friday
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 chances (30-50%) for snowfall totals in excess of 18"
through Friday.


...Northern New England...
Day 2...

Moisture streaming north out ahead of the Midwest winter storm
will be paired with increasing 850-700mb WAA aloft that produces
another round of precipitation. High pressure over Quebec will help
to lock in sub-freezign wet bulb temps from the White Mountains
northward through interior Maine, allowing for yet another mixed
wintry precipitation Thursday afternoon and lingering through
Thursday night. Snow will be the primary precipitation at the onset
in northern Maine, but even there it will flip over to a wintry
mix Thursday night with both sleet and freezing rain into Friday
morning. Eventually, strong low-level WAA will erode the sub-
freezing temperatures at the surface and precipitation will change
over to plain rain late Friday before ending overnight. Prior to
the changeover to rain, WPC probabilities for at least a tenth of
an inch of ice are moderate (40-60%) over the White Mountains and
along the northwestern Maine/Quebec border. Snow will really be
limited to just the Allagash where WPC probabilities for at least 4
inches are 20-40%.


...Northern Plains to the Upper Midwest...
Day 2.5-3...

The relatively progressive pattern across the CONUS will introduce
another round of potentially impactful snow to the Northern Plains
to the Upper Midwest Friday into Saturday. A slower moving 500mb
closed low over WY will generate healthy PVA aloft and increased
700mb Q-vector convergence over the northern High Plains early
Friday. 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. The area of low pressure will track
northeastward through Iowa and cross into WI by the end of this
forecast period (12Z Sat), though there is spread in the speed of
the low. Snow will remain on the northwest side of the low over the
Dakotas to northern MN but an area of mixed precip (sleet/freezing
rain) is again likely over parts of southern MN into WI and the
U.P. of Michigan.

WPC probabilities show a large swath of at >50% probability for at
least 4 inches of snow from northeast WY and southern/southeastern
MT through northern SD and southern ND east-northeastward to
northern MN. Given the slower progression of the upper low and
likely banding associated with this storm, snowfall rates >1"/hr
for a prolonged period could result in localized amounts exceeding
12" -- WPC probabilities show 20-40% chances in southern ND into
northern SD. Farther east, WPC probabilities for at least a tenth
of an inch of ice are 10-40% over southeast SD/southwest MN but
40-60% over northern WI into the U.P. of Michigan where most of the
precipitation will fall overnight Friday into early Saturday.
Changes to the forecast are likely but this system will likely have
impacts for much of the region, especially those who see a wintry
mix from the prior system later today/Thursday.


Fracasso/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