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FOUS11 KWBC 240813
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
313 AM EST Mon Nov 24 2025

Valid 12Z Mon Nov 24 2025 - 12Z Thu Nov 27 2025


...Northern Rockies...
Day 1...

Shortwave over Washington this morning will carry a cold front
through the Northern Rockies today. The strongest height falls will
cross through northwestern MT around Glacier NP with modest snow
above 5000-6000ft. WIth the moisture feed stretched back (but
weakening) to the Pacific, snow will fall as far south as the
Bitterroots and into northwestern WY where amounts will be lower (a
few inches). Snow will taper from west to east this afternoon
through this evening as the cold front makes steady progress
through the region. WPC probabilities for at least 8 inches of snow
are >50% above about 5000ft.


...Pacific Northwest/Northern Rockies...
Days 2-3...

The next Pacific system moves into western WA on Tuesday at the
nose of an 140kt 250mb jet. Colder air in place ahead of the
moisture may support some spotty freezing rain along the leeward
slopes/valleys of the Cascades and in the valleys of the Columbia
River Basin over northern WA. Snow levels will gradually rise as
the warm front lifts through Tuesday night into early Wednesday,
but the surface front will takes longer to cross the Cascades
rather than the more robust 700mb WAA nose that support the
potential for icy conditions east of the Cascades. Thanks to a
longwave trough firmly entrenched over the North Pacific, an
extended moisture fetch into the the Pacific Northwest will support
a more or less continuous stretch of mountain snow over the
Cascades and downstream into the Northern Rockies through the end
of this forecast period (then continuing into the medium range).
Snow levels will vary, starting around 2000-4000ft then rising to
around 5000-7000ft as milder air moves in. WPC probabilities for at
least 8 inches of snow are >50% above about 5000ft. Both
Snoqualmie and Stevens Pass may see multiple inches of snow before
snow levels rise above the passes early Wednesday.

...Northern Plains/Upper Midwest/Upper Great Lakes...
Days 1-3...

The shortwave trough exiting the Northern Rockies this afternoon
will move into the northern High Plains tonight. The upper jet
across the US/Canada will sharpen and support a strengthening area
of low pressure that will move from the Plains to the Upper Midwest
and western Great Lakes over the next few days. Tonight, an 850mb
low will form along a strengthening 925-850mb front over central
ND, while a narrow inverted trough axis forms on its western flank.
By 12Z Tuesday, bands of moderate to heavy snow are likely from
northeastern MT to central ND with increasingly gusty winds as the
low pressure strengthens. Tuesday afternoon the low over
southeastern MN will start to deepen quickly as the mid-level
shortwave starts to close off, allowing a TROWAL to form on the
western side of the storm. This could allow for >1"/hr snowfall
rates along with gusty winds over 30mph, causing blowing/drifting
snow. Some areas closer to Lake Superior and over central MN will
see marginal temperatures and snow may not accumulate quickly if
the rates are not high, though colder air will eventually win and
change all areas to snow overnight into early Wednesday as the low
moves into the U.P. of Michigan and deepens into the mid 990s mb.
By Wednesday night into early Thursday, the system will reach its
peak intensity over Ontario and take the bulk of its snow with it.
However, northerly to northwesterly flow will transition the lake-
enhanced snow to lake effect snow over northern WI into the U.P.
where the 850-lake temperature difference will be >15C (-10 to -14C
at 850mb and a lake temperature around 5C). Lake effect snow will
eventually break out across the rest of the Great Lakes by Thursday
morning and continue into the medium range period.

WPC probabilities for at least 4 inches of snow are >50% from
northwestern ND to central MN then eastward through the Arrowhead,
northern WI, and across much of the U.P. of Michigan. Within this
areas, probabilities for at least 8 inches of snow are >50% over
northeastern MN due to the synoptic system itself. Across northern
WI and into the U.P., the combination of synoptic snow and then
lake effect snow will boost totals well over a foot. There, WPC
probabilities for at least 18 inches of snow are >50% from near
Ironwood northeastward across the northern portion of the U.P. near
the Huron Mountains.

The probability of significant ice across the CONUS is less than
10 percent.

Fracasso

$$