Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
442 AM EDT Tue Apr 26 2022

Valid 12Z Tue Apr 26 2022 - 12Z Fri Apr 29 2022


...Pacific Northwest through the Northern Rockies ...
Days 1-3...

A stalled upper low centered over the Queen Charlotte Sound
maintains a steady stream of shortwave troughs through the Pacific
Northwest through at least Friday. Height falls and increased
moisture will bring renewed chances for snow for the elevations
generally above 3000 ft across the WA/OR Cascades into the
Clearwater and Salmon River Mountains of ID today. Day 1 WPC
probabilities for over 4" are moderately high there with isolated
totals above 8 inches possible.

A pair of shortwave troughs currently west of the upper low will
push across the PacNW coast Thursday before tracking to the
northern Rockies by Friday morning. Pacific moisture accompanying
the troughs along with Gulf-sourced moisture streaming up the
length of the Plains to allow a broad swath of moderate to locally
heavy precip to the northern Rockies Thursday night with a focus
likely on north-central ID and western MT. Snow levels over the
PacNW are expected to be around 3000ft and around 5000ft in the
northern Rockies. Day 3 probabilities for over 6" are moderate
from the OR Cascades to across these areas of ID/MT. Eastern
slopes of the MT Rockies look to get enhanced snowfall from the
increased moisture from the Plains.


...Northeast...
Days 2/3...
Shortwave energy will deepen as it crosses the Great Lakes today
and the Northeast Wednesday. A reinforcing impulse sends the
trough around the low into a negative tilt Wednesday night with a
deeper low then expected to linger just east of Maine Thursday and
Friday. The surface low that develops just off the New England
coast tonight will track along an existing frontal boundary and
deepen before lingering near the Bay of Fundy Wednesday into or
through Friday. Moisture thrown back around this low and across
Maine/Northern New England will interact with favorable forcing
for ascent to produce initially higher elevation moderate snow
across interior sections of northern New England with Wednesday
evening snow levels around 1500ft over the White Mtns.  However,
as the system occludes and stalls Thursday wrap around snow
showers linger across northern Maine where some of the guidance is
bullish with totals with snow levels dropping to near sea level.
Both Days 2 and 3 WPC probabilities for over 4" are moderate over
far northern NT/NH/ME.


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


Jackson