Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
221 PM EDT Fri Mar 13 2026

Valid 12Z Fri Mar 13 2026 - 12Z Mon Mar 16 2026

...Northern High Plains through the Upper Midwest...
Days 1-3...

...Blizzard likely this weekend with widespread major impacts and
record-breaking snowfall for portions of the Upper Midwest and
Great Lakes...

Guidance is consolidating around a rapidly strengthening low which
will develop in the lee of the Rockies Saturday and then track
east through Sunday to the Mississippi Valley, then turn northeast
Monday before occluding and then exiting. While the primary low is
going to be the one that brings the most substantial impacts, this
system will, in reality, driven by two distinct surface lows
embedded within the amplifying mid-level pattern and accompanying
coupled jet streaks.

The event really has already begun across the High Plains of
Montana as moisture streaming onshore within an impressive IVT
plume (atmospheric river) continues to push well inland leading to
a surge in PW/column moisture across the northern Plains. The
accompanying upper jet streak arcing zonally across the region
working in tandem with a surface stationary front will cause
snowfall to continue to spread ESE-ward. Overall ascent during D1
across this area appears modest as noted by omega fields and
regional soundings, but the impressive PW anomalies (nearing +2
sigma) will support periods of moderate snowfall from MT through
parts of SD. The heaviest accumulations are likely in the higher
terrain, with otherwise modest accumulations expected D1. Where the
heaviest snow occurs, generally just east of the Continental
Divide, WPC probabilities are high (>70%) for at least 4 inches of
snow for much of central and southern MT, with locally more than 8
inches possible in the Little Belt range.

The more significant portion of this event begins Saturday as lee
cyclogenesis begins in more impressive fashion east of CO/WY. A
shortwave digging onshore the British Columbia coast tonight will
begin to amplify as it digs into the Central Rockies Saturday
night. The rapid amplification of this shortwave will drive
impressive height falls downstream, with impressive jet streak
intensification occurring as a result. The overlap of height falls
with this jet development will lead to a rapidly deepening surface
low tracking from CO to IA before 12Z Sunday. As the jet begins to
kink southward, it will continue to produce heavy snow, with an
expansion across MT due to mid-level divergence downstream of the
approaching shortwave. At this time the snowfall rates should
become more intense through 00Z/Sun across MT, with additional
snowfall of 4+ inches possible (50-70%) for much of the eastern
half of the state.

After 00Z Sunday is when this event truly becomes a major winter
event with widespread considerable impacts. As the surface low
continues east from the Central Plains it will encounter dual
moisture streams, one from the decaying AR pushing east, and a
second as the theta-e ridge begins to arc northward on intensifying
WAA/southerly flow out of the Gulf. The overlap of robust deep
layer ascent with maximizing moisture return will deepen the low
substantially, and help expand a considerable precipitation shield,
with heavy snow arcing from SD through the Great Lakes by Sunday
morning, and then slowly pivoting northeast while continuing
through D3 as the surface low moves into Ontario by 00Z/Tuesday.

The synoptic setup is extremely favorable for a classic Midwest
winter storm with widespread intense snowfall. Embedded bands
with snowfall rates of 1-3"/hr are expected as reflected by high
potential for CSI and even CI in model cross-sections Sunday aftn
into Monday which drives intense omega into the TROWAL. Although
guidance has trended north, there is high confidence in a
laterally translating band of heavy snow from SD into MN Sunday
morning, with the environment transiting into one that matches the
conceptual model for a pivoting band over eastern MN and WI Sunday
evening into Monday, It is in this area where the heaviest snowfall
is expected, and potentially record, or near- record 2-day
snowfall is possible from eastern MN through WI and northern MI.
Elsewhere, snowfall rates of 1"/hr or more are still likely at
times, just with lesser duration. These snowfall rates combined
with gusty winds reaching up to 60 mph will create blizzard and
near- blizzard conditions and whiteouts, with major to extreme
impacts progged by the recent WSSI-P. Even in areas that get lower
snow totals, the blowing snow potential will still result in
difficult travel, and it is likely that most forms of
transportation will be treacherous at best, and impossible at
worst, through the event across a large area from Montana to
Michigan, and everywhere in between.

2-day WPC probabilities ending 12Z Monday are impressive, and
suggest a high likelihood (>70%) for at least 12 inches from the
Buffalo Ridge eastward through the Twin Cities, across much of WI,
and through all of the U.P. of MI. Within this axis, WPC
probabilities for at least 24" are already above 50%, and some
locations may approach 3 feet before the event winds down Tuesday.
Outside of this axis of heaviest snow, a broad swath of at least 6
inches is likely (>70%) from far western SD through central IA and
northeast into central MI. Similarly impressive, the 07Z NBM 5%
probabilities (meaning a 95% chance of seeing more), show amounts
over a foot from Central Wisconsin around Wausau east to north of
Green Bay, along the north shore of Lake Michigan over to the
Straits of Mackinac.

Finally, on the S/SE side of this snowfall swath, an axis of mixed
precipitation is likely, leading to icing accretion from central IA
through southeast WI and into lower MI. The most significant icing
is expected for lower MI where WPC probabilities for at least 0.25"
of ice are between 30-50%.

This storm could result in record snowfall in some places, and
with SLRs being slightly below climo, combined with the strong
winds, power outages and long-lasting impacts are expected. For
these reasons, Winter storm key messages are in effect, and are
linked below (Key Message 1).


...Cascades Through The Northern Rockies...
Day 1...

...Washington Cascades Major Winter Storm continues today...

An atmospheric river (AR) will wane tonight as an area of IVT with
around 500 kg/m/s continues to advect inland into the Pacific
Northwest and weakens. This AR will sink south into Oregon and
weaken overnight. Associated moisture already inland over the
Northern Rockies will continue the heavy snow into tonight,
tapering off from west to east.

There is high confidence in heavy snow tonight across the Northern
Rockies before precipitation wanes on Saturday with much lighter
snow. The more challenging aspect is what will happen with snow
levels across the region. As a surface cold front digs south in
conjunction with an upper level shortwave, snow levels will crash
across the Oregon Cascades and Idaho Panhandle, but with much
lighter precipitation during that transition in Oregon. In Idaho
and points south and east, the moisture will be slower to exit (as
there will be more of it as remnants of the A.R. This suggests
that considerable impacts will continue at the higher elevations of
the Northern Rockies, with lesser snowfall and impacts expected
across the Oregon Cascades.

This is reflected by WPC probabilities that show at least 4 inches
of additional snowfall D1 in the Blue Mountains, the Bitterroots,
the higher elevations of NW WY near Yellowstone NP, and the
Sawtooth/Salmon River ranges. By Saturday, snowfall persisting
across the Cascades wanes rapidly leaving just light additional
accumulations, but heavy snow will continue across the Wind Rivers,
Absarokas, Tetons, Big Horns, and other neighboring terrain where
WPC probabilities predict a high risk (>70%) for 8+ inches of snow.


...Great Lakes into the Northeast...
Day 1...

Intense but compact low pressure will continue crossing the Great
Lakes into the Northeast tonight and Saturday, bringing blizzard
and near-blizzard conditions to many areas. This low is being
driven by a potent but progressive shortwave which is progged to
continue driving northeast off the coast of Maine by Saturday
afternoon. The accompanying surface low over MI will picks up
speed and race east into New England Saturday before exiting into
the Canadian Maritimes.

As the low moves into the Northeast tonight, resurgence of WAA
will expand precipitation into New England, and a secondary low may
develop near the coast of ME Saturday morning. Total forcing for
ascent and available moisture will likely be less than areas
upstream (in the Great Lakes), but periods of heavy snow both
within WAA and along an inverted trough/occluded front upstream
from the secondary low pressure will result in areas of heavy
snowfall with rates again potentially reaching 1"/hr. WPC
probabilities across the Northeast are as high as 80% for 4+ inches
in the Tug Hill and southern Adirondacks, with probabilities
reaching 40-60% for the Chautauqua Ridge, and parts of the higher
terrain of VT/NH/ME. A local maxima is also possible along the
coast and interior mountains of ME where onshore flow ahead of the
secondary low pressure advects higher moisture onshore.

Wegman/Weiss


...Winter Storm Key Messages are in effect for the blizzard into
the upper Midwest and Great Lakes this weekend through Monday.
Please see current Key Messages below...

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