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

Valid 12Z Fri Apr 08 2022 - 12Z Mon Apr 11 2022

...Pacific Northwest to the Northern High Plains...
Days 1-3...
A cold front associated with a well-defined mid-to-upper level
shortwave is forecast to move onshore later this morning before
sweeping south and east across the Northwest into the northern
Rockies later today into the overnight, and then into the High
Plains by tomorrow morning.  While moisture with the system is
limited, it will mark the onset of significantly colder
temperatures across the region.  By late today and continuing
through the overnight, snows levels are expected to drop notably
across the region -- dipping below 1000 ft across much of
Washington, Oregon, northern Idaho, and western Montana by
tomorrow morning.  Additional decreases are forecast both Saturday
and Sunday night, with levels dropping below 500 ft across many
areas both nights.  While widespread heavy precipitation is not
expected with the front, northwesterly flow its wake with embedded
energy aloft will likely support showers through Sunday before a
developing closed low begins to move onshore Monday morning. 
Widespread snow accumulations of 8-12 inches, with heavier amounts
across the higher peaks, are likely for the Olympics, and the
Washington and northern Oregon Cascades.  With snow levels
plunging, 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 also possible
farther to the east across the higher elevations of the Blue
Mountains and the northern Rockies from northern Idaho and
northwestern Montana to northwestern and north-central Wyoming.

...Western Great Lakes to the Central Appalachians...
Days 1-2...
Northwesterly flow on the backside of a deep closed low that is
slowly drifting east across the western Great Lakes will continue
to support lake effect snow showers, with some additional locally
heavy amounts possible along the western to central U.P. of
Michigan today.  Showers are expected to diminish as the low
begins to gradually fill and lift out over the weekend. 
Meanwhile, deep cyclonic flow will support snow showers over the
central and southern Appalachians, with light accumulations
possible across the higher elevations today and tomorrow, before a
shortwave ridge begins to shift east across the region on Sunday.

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

Pereira