Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
340 PM EDT Thu Apr 14 2022

Valid 00Z Fri Apr 15 2022 - 00Z Mon Apr 18 2022

...Central West Coast region to the Northern Rockies...
Days 1-3...

An upper level low will continue to have staying power over the
Pacific Northwest through early Friday as it becomes strung out
along the U.S.-Canada border and is eventually reinforced by an
approaching shortwave trough set to reach the West Coast Saturday
morning. This will maintain a cold and unsettled pattern across
the region through the upcoming weekend. The ongoing snow over the
northern Sierra and into the northern Rockies under an area of
modest upper level diffluence will gradually wane on Friday.
Probabilities for greater than 8 inches of snow are over 50% in
the Wind River and Teton Range of WY. Following a brief lull, a
slightly stronger disturbance reaches northern CA Friday evening
and brings a heavier rounds of snow that will likely affect the
southern Oregon Cascades as well as the northern CA ranges and the
Sierra. Snow levels on Saturday morning will likely drop to around
3000-4000 feet, with moderate accumulations (over a foot) found
above into the high terrain. The low-mid level moisture plume will
track eastward across the Northern Rockies through the day
Saturday, with the heaviest snow (over 8 inches) found in and
around the Sawtooth Mts of ID and the ID Panhandle.

...Northern Plains...
Day 3...

By Sunday, the shortwave trough entering northern CA will help
steer a northern stream trough into the Pacific Northwest and
eventually the northern High Plains. Along with the associated
height falls, a surface low should develop near the northern
Wyoming Front Range and track across the Dakotas through Sunday
afternoon. There remains some latitudinal spread with this surface
low, the GFS and NAM being farther north and the CMC and ECMWF
farther south. WPC favored the more southerly track given upstream
trends and the more progressive upper-level pattern during this
time frame. Moist advection ahead of the trough is likely to lift
into a TROWAL and lead to relatively low SLRs, with the April sun
angle potentially lowering accumulations as well. Currently,
probabilities of at least 4 inches of snowfall between 00z 4/17
and 00z 4/18 are rather high from northeast MT to central ND
(40-70%). Probabilities for at least 8 inches in central ND are
between 10 and 30%. Much of this snow will occur over areas that
recently experienced blizzard conditions and over a foot of snow
earlier this week.

For Days 1-3, the probability of 0.10 inch or more of ice is less
than 10 percent.

Snell