Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
343 PM EDT Mon Oct 09 2023

Valid 00Z Tue Oct 10 2023 - 00Z Fri Oct 13 2023

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

A trough pushing across the PacNW coast this afternoon is ushering
in onshore flow and moderate precip. Snow levels drop from around
8000ft this afternoon to 5000ft tonight with a few inches likely
on the highest Cascades/Olympics only.

A deep low continues to shift east, reaching Vancouver Island late
Tuesday. A preceding atmospheric river pushes ashore Tuesday
morning with snow levels rising back to around 6500ft in moderate
to locally heavy precip. Again, heavy snow is limited to the
higher Cascades.

Snow levels settle around 6000ft under the upper low as it crosses
WA through Wednesday with moderate Day 2 probabilities for over a
foot on the high Cascades.


...North-Central Rockies...
Day 3...

A fairly deep upper low that reaches the Olympic Peninsula Tuesday
night weakens/opens into a trough Wednesday as it pushes southeast
over the northern Intermountain West. However, a reinforcing
trough from the Pacific Northwest Wednesday night will allow the
low to reform over the CO/WY/UT border by Thursday morning. By
this time, the lee-side low will be developing and shifting ENE
from CO with Gulf moisture wrapping around the developing low
pressure system. Generally disorganized precip develops Wednesday
over the north-central Rockies with snow levels initially 9000+
ft, but drop to around 7000 ft by early Thursday as the core of
the upper low settles over the region. The colder temps combined
with a lingering surface trough will enhance precipitation,
particularly across portions of WY. WPC probabilities for Day 3
(00Z Thur-00Z Fri) for 6"+ are moderately high for the Wind
Rivers, Absarokas (into MT), Bighorns, Laramie/Snowy Ranges and
the ranges of north-central CO. Orographic enhancement should help
rates get heavy enough for significant impacts from this early
season event.

The low then deepens further Thursday night which could lead to a
slow moving/prolonged event that likely gets cold enough for snow
for stripes over the High Plains of WY into Neb/SD. More about
that in the coming days.


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

Jackson