FOUS11 KWBC 010805
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
305 AM EST Sat Mar 1 2025

Valid 12Z Sat Mar 01 2025 - 12Z Tue Mar 04 2025


...Great Lakes through the Northeast...
Day 1...

The winter storm responsible for periods of heavy snow in parts of
northern Michigan marches east into southern Ontario today. Periods
of snow will stick around from the White Mountains to northern
Maine this morning. Following a break in the snow this morning, the
passage of a strong Arctic front paired with a deep upper trough
approaching from the west will provide a source of lift aloft.
Combine increasing surface-based heating that steepens low-level
lapse rates, and the stage is set for scattered snow showers and
snow squalls from the Great Lakes and Upper Ohio Valley on east
through the Interior Northeast throughout much of the day Saturday.
Plummeting temperatures could aid in rapid snowfall accumulations
in wake of the cold frontal passage, but there is also a concern
for bursts of heavy snow and gusty winds that cause dramatic
reductions in visibility for those on roadways and for aviation.
Travelers on roadways should be sure to have a reliable way to
receive snow squall warnings should they be issued. Snow should
taper off not long after sunset Saturday evening, although some
residual lake-effect snow showers may stick around into parts of
Saturday night. WPC probabilities through 06Z Sunday show moderate-
to-high chances (50-70%) for >4" of additional snowfall in the Tug
Hill, the White Mountains, and far northern Maine.


...California & Great Basin...
Days 2-3...

A closed upper-low tracking into California on Sunday will direct
an IVT topping out around 250 kg/m/s at the Sierra Nevada and
Southern California ranges. While SWrly low-level winds may provide
some marginal upslope flow enhancement, this IVT is not
particularly strong, thus limiting most heavy amounts to the
highest/more remote elevations. Snow levels are expected to be as
low as 4,000ft from the Sierra Nevada on east into the Great Basin,
but the heavier amounts will generally be confined to elevations
above 6,000ft. Snow will fall heaviest over the Sierra Nevada and
as far north as the Shasta/Siskiyou Sunday afternoon and into
Sunday night. As the upper low approaches Sunday night, Pacific
moisture will spill over into the Great Basin with moderate-to-
heavy snowfall along the 6,000-7,000ft ridge lines of central
Nevada Sunday night and into Monday. Moisture and a potent upper
low will then eventually reach the central Rockies late Monday. WPC
probabilities depict moderate-to-high chances (50-80%) for
snowfall >8" at elevations above 7,000ft in the Sierra Nevada
through Monday morning. Similar moderate-to-high chance
probabilities for >6" of snowfall exist along the ridges of
central Nevada through Monday evening.

...Northern & Central Rockies to the Central Plains...
Day 3...

The upper low responsible for the mountain snow in the mountain
ranges of California and the Great Basin will make its way into the
Central Rockies on Monday. Falling heights and residual Pacific
moisture will support moderate to locally heavy snowfall in the
Wasatch, Uinta, southern Wyoming Rockies, and northern Colorado
Rockies. WPC probabilities show moderate-to-high chances (50-80%)
for snowfall >6" at elevations above 9,000ft. Farther north,
temperatures will gradually cool as a cold front ushering in
Canadian high pressure moves south. Lingering Pacific moisture,
combined with weak easterly upslope flow will allow for light-to-
moderate snowfall in the Northern Rockies between Monday afternoon
and Tuesday morning.

There remains a fair amount of spread regarding the snow potential
in the Central and Northern Plains. The synoptic-scale jet stream
setup is generally agreed upon; a strong jet streak over northern
Mexico will place its divergent left-exit region over the central
Plains Monday night. Along with strong PVA ahead of the 500mb low
in the Rockies will result in cyclogenesis in lee of the Colorado
Rockies that will organize and strengthen a surface low rather
quickly by Tuesday. Where guidance differs are on the storm track,
the rate at which the storm deepens, and the extent to which the
colder air to the north is in place soon enough to result in a
swath of heavy snow in the Northern Plains. The GEFS members are
generally are a little faster, farther north, and deeper with the
storm by 12Z Tuesday compared to the ECENS which is slower and
farther south. The one thing these ensembles have in common is
focusing on the Palmer Divide and over the Raton Pass with strong
enough NErly upslope flow, along with strong dynamic cooling aloft
to support heavier snowfall. Even in this case, however, any faster
storm motion could mean less snowfall, and the opposite for
heavier snow should the storm slow down. Through 18Z Tuesday, WPC
probabilities show moderate chances (40-60%) for snowfall >4" along
the Palmer Divide, but lesser chances (10-20%) along Raton Pass.

With a lack of sufficiently cold air east of the Rockies, snowfall
potential will be more directly tied to the deformation axis
placement and dynamic cooling aloft from the Denver metro on north
and east. Residents in the Central and Northern Plains will want
to monitor the forecast closely over the weekend as this is a
complex storm system whose final storm track is not resolved yet.


Mullinax




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