Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
448 AM EDT Tue Oct 10 2023

Valid 12Z Tue Oct 10 2023 - 12Z Fri Oct 13 2023

...Pacific Northwest...
Days 1-2...

Mid-upper level troughing moves onshore the Pacific Northwest
through today and tonight and the favored left exit region of the
110+ kt jet will provide plenty of forcing for ascent across the
region. Snow levels will gradually drop through this morning to
under 6000 ft before rising again later today to around 6500 ft.
This will really limit the greatest snowfall accumulations to the
highest peaks of the Cascades where WPC snow probabilities for at
least 4 inches are high. By late tonight into Wednesday, the core
of the upper level low moves overhead and snow levels fall back
toward 6000 ft.


...North-Central Rockies...
Days 2-3...

Strong mid-upper level trough moves through the Intermountain West
and Rockies later Wednesday into Thursday, eventually closing off
in the lee of the Rockies early Thursday. Favorable forcing for
ascent, aided by the left exit region of the upper jet streak,
combined with the orographic upslope, will bring widespread
precipitation to the North-Central Rockies. As a cold front sweeps
eastward, snow levels will fall from around 9000 ft to 7000 ft,
leading to greater snowfall accumulations for the higher peaks.
Meanwhile, a strong surface low is expected to develop in the lee
of the Rockies, with greater frontogenesis and orographic upslope
across portions of the CO Rockies northward into Wyoming and SD
Black Hills. This will enhance precipitation, particularly across
WY. The WPC probabilities for at least 8 inches are moderate
(40-60 percent) for the northern CO Rockies, through WY, and into
south-central MT ranges. The Big Horns have above 50 percent
probabilities for at least 12 inches. This is shaping up to be a
potentially significant early season event for some locations,
with the WSSI-P showing 40-60 percent probabilities for moderate
impacts across the WY mountains and SD Black Hills, driven
primarily by the snow rate and snow load, which makes sense given
the high moisture present with this system. It's possible by the
end of Day 3 (Thursday night), as the core of the upper level low
moves into the High Plains, wet snow may reach the lower
elevations of the eastern Wyoming and western Nebraska.


Days 1-3, the probability of significant ice accumulation across
the contiguous U.S. is less than 10 percent.

Taylor