FOUS11 KWBC 290823
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
423 AM EDT Sat Mar 29 2025

Valid 12Z Sat Mar 29 2025 - 12Z Tue Apr 01 2025

...Central/Northern Plains, Upper Midwest, and Northern Great Lakes...
Days 1-2...

Long-duration ice storm to impact northern WI through the northern
MI L.P. and much of the central/eastern U.P. through Sunday, while
moderate to heavy snow is likely from SD/Neb through far northern
WI and along the lakeshore of Lake Superior.

A negatively tilted upper trough will cross the Intermountain West
today and usher potent SWrly flow into the north-central U.S.,
while a leading mid-level shortwave ejects into the central Plains
by this afternoon. This leading shortwave is associated with
leeside cyclogenesis along the CO/KS border and an attached sharp
stationary front extending east-northeast through the Midwest and
Great Lakes. As moisture overruns this frontal boundary and
expansive high pressure stretches across Canada, a wintry mix of
snow, sleet, and freezing rain is likely this weekend.

Snowfall is forecast to begin across western Neb into the Black
Hills and south-central SD by this afternoon associated with the
mid-level low crossing overhead leading to sufficient convergence
and bands of snowfall capable of containing 1-2"/hr rates. These
rates will be imperative to achieving heavy accumulations as
boundary layer temperatures start out well above freezing. The 00z
HREF depicts the best chances for these intense snowfall rates are
along the western and central SD/Neb border centered near the Pine
Ridge Reservation. Snowfall rates will likely lower while the
northern precipitation shield expands east-northeast in response to
the progressing surface low and forcing becoming more stretched in
an east-west direction. Moderate snow will extend across SD,
central MN, and towards far northern WI and the MI U.P. by tonight.
There has been some latitudinal uncertainty regarding this swath
of snow, with 00z guidance coming in a touch south. Regardless, WPC
probabilities for at least 4" of snow are 30-60% for this region,
with localized pockets up to 80%. Meanwhile, the heaviest snowfall
from this system is most likely from near or just south of Duluth,
MN eastward along the lakeshore of Lake Superior from far northern
WI into the MI U.P. due to snow remaining the dominant ptype
throughout the event. Here, WPC probabilities for at least 6" are
high (60-80%).

South of the heavy snow axis a corridor of impactful sleet and
freezing rain are forecast to stretch from northern WI through much
of northern MI. A prior storm has already led to a corridor of ice
across this region and precipitation may linger continuously today
across northern WI/MI until a resurgence tonight through Sunday.
High pressure (~1030mb) over James Bay will continue to usher in
cold northeasterly flow as the surface low tracks across southern
WI on Sunday. Ice accretion may be limited during daytime hours
given the late-March sun angle, but with the bulk of the wintry mix
occurring Saturday night there is the potential for significant
ice accumulations. WPC probabilities for at least 0.25" of freezing
rain are highest (60-90%) across parts of northern WI and the
northern MI L.P., with chances for >0.5" at 30-60%. Medium
probabilities (30-60%) for at least 0.25" also extend into the
central/eastern MI U.P. as well as into parts of northwestern WI to
the border of MN. In addition to the freezing rain threat, some
areas from northern WI to the MI U.P. could experience over 1" of sleet.

...Northeast... Days 1-2...

Prolonged wintry mix expected across the Interior Northeast through
New England this weekend, including the potential for heavy icing
before above freezing temperatures return on Monday.

An initial pulse of heavy precipitation is swinging through
northern NY and New England this morning, including heavy snow up
to 1"/hr until around 14Z across northern VT into central/northern
NH. This snowfall is a result of a jet max passing to the north of
New England and where 925-850mb WAA is strongest, which quickly
wanes later today.

South of this heavy snow threat between the northern Adirondacks
and much of central/southern VT and NH, 850-750mb warm nose allows
for a transition zone of sleet/freezing rain. After the brief
burst of heavier precip this morning, forcing weakens and there is
left a weak stream of moisture overrunning a CAD signature due to
the strong High situated over the James Bay and elevated PWs (above
the 90th climatological percentile per the NAEFS SAT) continuously
advected from the WSW. WAA gains latitude by Sunday as the Great
Lakes low pressure strengthens and tracks northeast into Canada by
Sunday night. Even with this storm track turning the entire northeast
eventually over to rain on Monday, a prolonged wintry mix this
weekend could lead to significant freezing rain amounts. Areas most
at risk for heavy icing include northern NY and the Adirondacks,
through the Greens and Whites of VT/NH, where CAD is likely to
remain longest.

WPC probabilities for >0.25" ice are 60-80% for the Thousand
Islands area, the northern Adirondacks and south- central VT/NH.
Probabilities for >0.1" ice extend as far south as the MA
Berkshires and northward along the White Mts through ME into Day 2.

...Northern/Central Rockies... Days 1-3...

An upper trough sliding eastward across the Intermountain West
today will maintain some Pacific moisture advection into the
northern/central Rockies while also interacting with a developing
low- to- mid level baroclinic zone to produce light-to- moderate
mountain snow this weekend. Precipitation coverage is expected to
peak on Day 1 as the upper trough moves through, with unsettled
weather continuing through Sunday across MT/WY due to the
relatively strong baroclinic zone being reinforced by high
pressure positions over southern Saskatchewan. Snow levels
beginning around 5000ft in the northern Rockies are forecast to dip
below 4000ft in some location by this evening. In the central
Rockies, snow levels will drop to 7000-8000ft in the Colorado
ranges and around 5000-6000ft across northern Utah. WPC Days 1-2
probabilities for >8" of snow are generally 40-70% over southwest
MT, the Absarokas and Wind River Range, and the Park Range and
Medicine Bow Mountains of northern CO.

By the end of Day 3/12z Tuesday, a strong closed upper low returns
to off the Pacific Northwest and extends a 160kt 250mb westerly
jet inland through the central Great Basin. Pacific moisture,
upslope flow, and increasing upper divergence to the north of this
low produces the next round of mountain snow across the
northern/central Rockies. Current WPC Day 3 probabilities for at
least 8" are 30-50% from southwest MT, western WY, into the
northern CO Rockies.

...West Coast through the Intermountain West... Days 2-3...

The next cold core low drifts toward OR, but remains offshore
Sunday through Monday. A broad plume of Pacific moisture shifts
inland Sunday and lifts northeastward with renewed enhancement
from an ejecting shortwave trough Sunday night producing heavy
precip over the northern half of CA Monday. Days 2-3 snow probs for
>8" are 50-90% in the southern OR Cascades, the Klamath/Trinity
Alps, and northern/central Sierra Nevada with snow levels of
5000-6000ft Sunday dropping to 4000-5000ft by Monday morning. Snow
also extends into the central/northern Great Basin Sunday night
through Monday, with snow levels falling below 4000-5000ft on Day 3
across the Idaho ranges and remaining around 5000-6000ft across UT/NV.

Snell
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