Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
333 AM EST Mon Mar 3 2025

Valid 12Z Mon Mar 03 2025 - 12Z Thu Mar 06 2025

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

A potent 500mb closed upper-low barreling through the
Intermountain West will generate exceptional divergence aloft while
modest 700-300mb moisture wraps around the northern and western
flanks of the closed low. The result is high elevation snow from
central Nevada on east through the Wasatch, the Uinta, as far south
as the Mogollon Rim, and east to the southern Wyoming and Colorado
Rockies. WPC probabilities show high chance probabilities (>70%)
for snowfall >6" in the Nevada ranges above 6,000ft, the Utah
ranges above 8,000ft, and northern Arizona ranges above 7,000ft.

By 00Z Tuesday, the 500mb low tracking across southern Colorado
will work in tandem with the divergent left-exit region of a
250mb jet streak to support lee cyclogenesis over the central High
Plains. As the closed low aloft strengthens at 700mb and 850mb, a
strong 50+ knot LLJ will direct a stream of low-level moisture
northward through the Southern Plains that wraps around the
700mb low. The northerly flow with embedded moisture aloft is
strong enough to the point that by 12Z Tuesday, there is a
northerly >200 kg/m/s IVT over eastern Colorado. This anomalous
moisture source, combined with the robust synoptic-scale
enhancement will support heavy snow in the Front Range of the
Colorado and southern Wyoming Rockies, and as far south as the
Palmer Divide. The Palmer Divide in particular is particularly at
risk for blizzard conditions Monday night into Tuesday morning as
700mb winds of 50-70 knots result in whipping wind gusts. WPC
probabilities show high chance probabilities (>70%) for snowfall
>8" in the northern Colorado Rockies above 9,000ft. Along the
Palmer Divide, WPC probabilities show moderate-to-high chances
(50-70%) for snowfall >6" through Monday evening. Snow should
taper off around midday Tuesday along the Front Range of the
Rockies.


...Central Plains to Upper Midwest...
Days 1-3...

...Powerful winter storm to cause widespread heavy snow and blowing
snow with localized blizzard conditions across the central Plains
from Monday night into Tuesday and then into the Upper Midwest
Tuesday night through Wednesday...

By 06Z Tuesday, a closed and potent 500mb low will track into
western Kansas with a rich plume of low-level moisture advected
northward by a >50kt LLJ over the Southern Plains. Moisture will
wrap around the deepening cyclone, resulting in strong 850-700mb
WAA that causes a narrow axis of moderate snow embedded within a
wind field that could produce >70mph wind gusts late Monday night
and into Tuesday morning. The upper-low takes a subtle dip south
and east along the KS/OK border midday Tuesday before tracking
northeast towards the Midwest Tuesday evening. The 700mb will will
track over the Kansas City metro by 00Z Wednesday and the pivoting
axis of best 850-700mb FGEN will pivot from eastern Nebraska and
northeast Kansas on northeast through Iowa and into the Upper
Mississippi Valley. The enhanced mesoscale forcing will be co-
located beneath a "kissing jets" setup; where the developing storm
system lies beneath the divergent left-exit region of a jet streak
over Texas, and beneath a strengthening jet streak over the upper
Great Lakes. Plus, 850mb and 700mb heights at this time over
eastern Kansas are below the observed heights for this time of year
in the CFSR climatology. With robust ascent aloft and strong
mesoscale forcing within the deepening TROWAL, the deformation axis
of heavy snow will be capable of producing up to 1"/hr snowfall
rates and whipping wind gusts of 50mph. While the band will be
progressive as it moves through eastern Kansas and eastern
Nebraska, that 3-6 hour wind of heavy snow can still cause
significant reductions in visibilities for motorists and aviation
Tuesday evening.

The storm then tracks through eastern Iowa Tuesday night with its
expansive deformation axis producing snow from the Kansas/Missouri
border on north through central Iowa and as far north as the
Michigan U.P.. Strong wind gusts topping 40 mph are possible in
these areas Tuesday night and into Wednesday. The heaviest snowfall
by Wednesday morning will be found across southeast Minnesota,
northern Wisconsin, and the Michigan U.P.. The Michigan U.P., in
particular, is most favored for heavy snow due to the help of
lake-enhanced snowfall and colder boundary layer temperatures.
Snowfall will be more difficult to accumulate during the day
Wednesday on the fringes of where it is snowing rather than beneath
the heaviest rates, but the blustery wind gusts still can cause
near whiteout conditions in some cases. In addition, the high
moisture content and lower SLRs from central and northern Wisconsin
to the Michigan U.P. suggests the combination of a heavy/wet snow
on trees and power lines could lead to some cases of power outages
and downed tree branches.

WPC probabilities shows moderate chances (40-60%) for snowfall >4"
from western and northern Nebraska to southern South Dakota. There
is then another swath of moderate-to-high chance probabilities
(40-70%) for >4" of snowfall from eastern Nebraska to northern
Iowa. Southern Minnesota on north and east through northern
Wisconsin and the Michigan U.P. sport 50-70% odds of snowfall
totals >6". There are some low chance probabilities (10-30%) for
localized snowfall totals >12" in parts of far northern Wisconsin
and along the Michigan U.P.. Overall, blowing snow will be the
most detrimental impact from the central High Plains to central
Iowa and southern Minnesota, while snow amount, snow load, and
blowing snow all make for a treacherous day of travel in portions
of the Upper Mississippi Valley Tuesday night and through
Wednesday.

...California, Great Basin, & Intermountain West...
Day 3...

Guidance is in agreement on an approaching upper-level trough off
the California coast that will interact with the subtropical jet in
the East Pacific. This interaction will produce a strengthening IVT
that tops out around 400 kg/m/s IVT at 12Z Wednesday and directs
its moisture well into the Southwest U.S.. By 00Z Thursday, the
IVT and its broad >200 kg/m/s footprint extends into the Wasatch
and Central Rockies. As the upper trough takes on a more negative
tilts along the California coast Wednesday afternoon and eventually
over the Great Basin Wednesday night, heavy snow will gradually
descend along the spine of the Sierra Nevada and into central
Nevada as well. WPC probabilities show high chances (>70%) for >12"
of snowfall at elevations above 9,000ft in the southern Sierra
Nevada with similar high-chance probabilities for >8" of snowfall
in the central Sierra Nevada. WPC probabilities also show some
moderate-to-high chance probabilities (50-80%) form snowfall totals
>4" in central Nevada on east to the Wasatch and Uinta through 12Z
Thursday. Periods of snow are forecast to continue across the
Intermountain West into Thursday.


Mullinax


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

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