Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
434 AM EDT Wed Apr 27 2022

Valid 12Z Wed Apr 27 2022 - 12Z Sat Apr 30 2022

...Northern Rockies to Northern Great Plains...
Days 2-3...
A pair of low amplitude shortwaves dig across the Pacific
Northwest on Thursday before shifting over the northern Rockies
Thursday night into Friday. As the system continues to amplify and
track east, lee-side cyclogenesis along the High Plains promotes
increased moisture influx to the eastern side of the northern
Rockies. Heavier snows develop across north-central ID and western
MT Thursday night and Friday under favorable upper jet forcing,
combining with upslope on the north side of a developing 700mb
low. Snow levels will generally be around 5000ft, though banding
and convective elements should easily lower these levels to
4500ft. A low pressure system develops over the north-central
Plains Friday night with banding with enough dynamic cooling to
overcome the marginal thermal environment and allow snow
accumulation on the northern Plains, in a swath likely similar to
the most recent snow there from northeast WY and up the MT/Dakota
border. Days 2/2.5 WPC probabilities for over 8" snow are
moderately high for most of the west-central MT ranges from the
Bitterroots to the Big/Little Belt Mtns along with the northern
Absarokas along with low values for the Bighorns of WY and the
Black Hills. As of now Day 3 probabilities for over 2" are 10 to
20% along the MT/Dakota border.


...Northeast...
Days 1-3...
A compact upper low will move across NY/New England today before
stalling over Maine/Nova Scotia tonight and into or through
Saturday. Low level frontogenesis overlapped by favorable upper
dynamics will support precipitation developing on the northwest
side of the low across northern New England today. As the air
column cools, rain changing to snow is expected this afternoon,
with snow, moderate at times continuing across northern portions
of Maine into Friday with light snow potentially lingering into
Friday night. Day 1.5 WPC probabilities for over 4" are moderately
high along the Maine/Quebec border where moderate 8" probabilities
are also featured. Probabilities for 4" decrease, but expand over
much of northern Maine for Day 2.

For days 1-3, the probability of significant icing greater than
0.25 inches is less than 10 percent.

Jackson