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

Valid 00Z Sun Mar 30 2025 - 00Z Wed Apr 02 2025


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

A negatively tilted 250-500mb trough axis working in tandem with
the strongly diffluent right-entrance region of a 250mb jet streak
will organize an emerging area of low pressure in the Midwest
tonight and into Sunday. Sufficiently cold temperatures are locked
in place to the north of the robust 925-700mb FGEN warm front that
is oriented W-E from northern MN to as far east as northern NEw
England. This is all thanks to a 1030mb+ high pressure system over
southeastern Canada that is supporting the ongoing icy setup. As
strong SWrly winds overrun the sub-freezing air-mass, a >0C warm
nose protruding into the 850-700mb will cause precipitation to
fall in the form of freezing rain and sleet throughout the Upper
Midwest, Upper Great Lakes, the northern Appalachians, and New
England through Sunday. While ice will be the more commonly
observed winter weather hazard, there will be snow beneath the
deformation zone on the northern and western flanks of the 850mb
low.

Periods of snow will be ongoing in the Sand Hills of Nebraska
and over southern South Dakota this afternoon with snow increasing
in coverage from the Upper Midwest to the Michigan U.P.. South of
the snow axis, freezing rain and sleet will be common in northern
Wisconsin, the eastern Michigan U.P., across the tip of Michigan's
Mitten, and as far east as interior New England. By Sunday morning,
most areas will begin to transition to rain with the exception
being northwest Wisconsin and the western Michigan U.P.. The
deformation axis will continue its swath of snow from southeast
Minnesota to central Wisconsin Sunday afternoon, but it will be
progressive and snow falling during the daytime hours will be
tougher to accumulate. Some lingering freezing rain is possible in
the eastern Michigan U.P.. and northern New England Sunday evening.
Snow within the deformation axis is continue over northern Michigan
Monday morning before finally exiting to the northeast over Ontario
by Monday afternoon.

WPC probabilities show moderate-to-high chances (50-70%) for >4"
of snowfall in parts of northern Nebraska, southern South Dakota,
eastern South Dakota, and central Minnesota. Farther east, similar
moderate-to-high chance probabilities are present for >8" of
snowfall in far northern Wisconsin and across the western and
central Michigan U.P.. In terms of freezing rain, WPC probabilities
show moderate chances (40-60%) for ice accumulations >0.5" in
northern Wisconsin, northern Michigan, and in Northeast mountain
ranges such as the Adirondacks, Green, and White Mountains. There
is an expansive area of moderate-to-high chance probabilities for
>0.25" of ice accumulation as far west as the MN/WI border and
across the southern tier of Michigan's U.P.. All of these areas can
anticipate hazardous travel conditions with the potential for
power outages in those areas sporting better chances for >0.50" of
ice accumulation.


...The West...
Days 1-3...

An active stretch of wintry weather from the West Coast to the
Front Range of the Rockies through Sunday. A pair of shortwave
troughs traversing the Rockies tonight will be responsible for
mountain snow from as far north and west as the Absaroka and
Bitterroots through the Wyoming ranges and on south to the Colorado
Rockies through early Sunday morning. As high pressure builds in
over the Canadian Prairies on Sunday, easterly upslope flow and
residual moisture aloft will foster additional mountains snow in
the Black Hills and Big Horns. Some lower elevations snowfall is
expected during the day on Sunday as well, but accumulations will
be minor due to the late season sun angle limiting accumulations.
WPC probabilities do depict moderate-to-high chances (50-70%) for
snowfall totals >6" in the highest elevations of the Absaroka,
Wind River, and northern Colorado Rockies.

By Sunday afternoon, focus shifts to an exceptional closed upper
low in the northeast Pacific that slowly makes its way east towards
the Pacific Northwest on Monday. Heavy high elevation mountain snow
(above 6,000ft in the northern CA ranges and above 5,000ft in both
the Cascade and Blue Mountains) will be underway, but as the upper
low inches closer to the Northwest U.S., falling heights and colder
temperatures aloft will cause snow levels to lower Sunday night and
into Monday. By 12Z Monday, NAEFS shows just about all mandatory
height levels listed are bottoming out below the 2.5 climatological
percentile while IVT values >500 kg/m/s are aimed at southern
California. From northern California to the interior Northwest, the
region will also be located beneath the divergent left-exit region
of a 200mb jet streak whose wind speeds (>130 kts) are above the
99th climatological percentile. With the IVT located farther south,
the best moisture advection and upslope enhancement will be seen
from California's Siskiyou and Salmon mountains on south and west
along the spine of the Sierra Nevada. By Monday afternoon and into
Monday night, the flood of Pacific moisture aloft will advance well
inland through much of the Intermountain West. Just about every
notable mountains range in the central and northern Rockies is
likely to see measurable snow Monday night into Tuesday. Meanwhile,
cyclonic flow around the upper low will still support ongoing
upslope snowfall in the central and northern California ranges
through Tuesday.

A very wintry few days are coming to the mountain ranges of the
western U.S.. Through 00Z Wednesday, WPC probabilities show the
northern ranges of California (Siskiyou, Salmon, Shasta) and the
length of the central and northern Sierra Nevada have high chances
(>70%) for snowfall totals >12". Most of these ranges above 6,000ft
are currently forecast to see localized amounts between 2-3 feet
through 00Z Wednesday. Farther inland, many Intermountain West
ranges (Sawtooth, Blue, Uinta, Bear River, Wind River, Absaroka,
Big Horn, and CO/WY central Rockies) are all likely to see snowfall
totals of 6-12" with locally higher amounts in these ranges as
well. Expect hazardous travel conditions for many road ways that
remain open in these mountain ranges.

...Northern Plains and Upper Midwest...
Day 3...

By Tuesday morning, the upper trough responsible for the barrage of
mountain snow in the West will position the 250mb jet streak's
divergent left-exit region over the Great Plains. Modest 500mb PVA
and strengthening WAA at low levels will give rise to lee
cyclogenesis east of the Rockies. Throughout the day Tuesday, a
strengthening LLJ, (NAEFS shows 850mb winds above the 90th
climatological percentile 18Z Tuesday from north Texas to the Red
River of the North), will deliver both increased moisture and
increasing WAA aloft. There also appears to be sufficiently cold
enough air present that precipitation will transition over from
rain to snow from the Black Hills on east across South Dakota and
as far east as central Minnesota by 00Z Wednesday. There are
ongoing differences in the position of this developing deformation
axis. All three deterministic guidance members (EC/GFS/Canadian)
along with the EC-AIFS all show this storm growing in strength and
size heading into Day 4, but they do this in different ways both
synoptically and on the mesoscale as well. The ECMWF EFI does show
a growing signal for a potentially disruptive winter storm from the
Dakotas on east across Minnesota and into the northern Great
Lakes. Both snow amounts, along with snow load and blowing snow are
likely to be hazards that the Northern Plains and Upper Midwest
contend with Tuesday night into Wednesday. Residents and those
traveling to/from these regions should keep close eyes on the
forecast as additional changes in the types of impacts, the
severity of those impacts, and where/when these impacts occur are
likely to fluctuate for the rest of the weekend.


Mullinax