Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
445 AM EDT Sat Apr 09 2022

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

...Pacific Northwest to the Northern High Plains...
Days 1-3...
A strong cold front continues to push southeast across the
northwestern corner of the CONUS this morning.  In its wake, deep
northwesterly flow with embedded energy aloft will support showery
and unseasonably cold weather today across the Northwest into the
northern Rockies.  Already low snow levels are expected to dip
further tonight, dropping below 500ft across much of Washington,
eastern Oregon, and the northern Rockies by tomorrow morning. 
Models show a fairly well-defined shortwave moving onshore,
supporting some organized precipitation along the coast from
Washington to the North Coast of California tomorrow morning. 
However, a greater chance for heavier precipitation is expected to
develop tomorrow night and continue into Monday as a closed low
forms offshore and moves inland.  As the low moves across the
region Monday and Tuesday, the GFS shows 500mb heights dropping
2-3 standard deviations below normal across the Northwest into the
northern Rockies.  With snow levels remaining low, minor
accumulations are possible across the lowlands and interior
valleys of Washington and Oregon.  Several inches are possible in
the higher elevations of coastal ranges, with heavy amounts of a
foot or more likely for the southern Washington and Oregon
Cascades.  A shortwave digging south of the low will support snow
spreading south from the Northwest California mountains into the
Sierra on Monday, with heavy amounts possible across the higher
peaks.

As the low continues to move east, accumulating snows are likely
to reach down to the valley floors of eastern Washington, Oregon,
and Idaho, with heavy accumulations possible for the northeastern
Oregon and central Idaho ranges.  Snow is expected to develop east
of the Divide across the northern High Plains Monday night into
early Tuesday.  Increasing upslope flow on the northwest side of a
low moving east of the Rockies, along with divergence aloft near a
coupled jet, will support heavy snows developing over the central
to western Montana ranges Monday night into Tuesday. 

...Upper Midwest...
Day 2...
A shortwave dropping into the Northwest later today is forecast to
move across the northern Plains tomorrow and then lift north,
assuming a negative tilt as it tracks across the Upper Midwest
Sunday night and Monday morning.  This dynamic system is expected
to support rain changing to snow across northern Minnesota late
Sunday into early Monday.  With the GFS continuing to back away
from its more amplified solution, it is now in better agreement
with the general model consensus of an inch or two or likely, but
with some potential for heavier amounts given the dynamics of the
system. 


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

Pereira