Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
438 PM EDT Fri Apr 08 2022

Valid 00Z Sat Apr 09 2022 - 00Z Tue Apr 12 2022

...Pacific Northwest to the Northern High Plains...
Days 1-3...

A cold front sweeping south and east across the Northwest marks
the onset of a return to wintry conditions across The West that
continues through the middle of next week. Snow levels are
dropping across the region, reaching 1000 ft across much of
Washington, Oregon, northern Idaho, and western Montana by late
tonight. These snow levels are maintained as cold air spreads
across the rest of the Northwest Saturday. Reinforcing troughing
brings the coldest air to the PacNW coast Saturday night with snow
levels there dropping to 500 ft into Sunday.

The combination of reinforcing waves likely results in a closed
low over WA or OR by Sunday night. The GFS and UKMET have been
bullish with this low and thus a faster/more northern solution
than the more open/positively tilted trough off the PacNW that is
slower in the EC/CMC. 12Z guidance still has a disconnect between
these two camps, though the EC/CMC did shift north with their QPF
solutions with the CMC (and perhaps more specifically the
CMC_regional) being the best compromise at this time for precip.
We will see if this trend toward a compromised solution between
these camps continues. Overall, a northern trend in the main
precip axis both over the Northwest Sunday night into Monday and
toward the northern High Plains Monday into Monday night is noted.
There is still the risk for a powerful winter storm to develop
early next week with strong winds and banded heavy snow.

Days 1-3 there is confidence in the heavy snow threat shifting
south from WA on Day 1 (high probs for over 6" in the Cascades),
into OR Day 2 (high probs for over 6" spread down to the central
OR Cascades) and along the OR Cascades for Day 3 with some
probabilities for over 6" into the northern Sierra Nevada. 2 to 3
feet is likely to fall along the entirety of the WA/OR Cascades
through the next 72hrs. With anomalously low snow levels, heavy
accumulations are likely for the northern Cascade passes, with WPC
probabilities indicating accumulations of 8 inches or more likely
by Sunday morning at both Snoqualmie and Stevens passes.  Locally
heavy accumulations are likely with a leading reinforcing impulse
coming off the building through in the PacNW on Day 2 across the
higher elevations of the Blue Mountains and the northern Rockies
from northern Idaho and northwestern Montana to northwestern and
north-central Wyoming and the Black Hills.


...Great Lakes to the Central Appalachians...
Days 1-2...

Northwesterly flow continues on the backside of a deep
closed/occluded low that is drifting across eastern Ontario this
afternoon will continue to support locally moderate lake effect
snow showers over the U.P. into this evening. Meanwhile, deep
cyclonic flow will support moderate to locally heavy snow showers
over the central and southern Appalachians tonight through
Saturday night. Day 1 snow probabilities for over 4" are
moderately high for the Allegheny Highlands of east-central WV and
for the Great Smokies.
Ridging the wake of this anomalously deep low begins to shift east
across the region on Sunday, cutting off the upslope flow.


For Days 1-3, the probability of significant icing of at least
0.25" is less than 10 percent.

Jackson