FOUS11 KWBC 240711
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
311 AM EDT Tue Mar 24 2026

Valid 12Z Tue Mar 24 2026 - 12Z Fri Mar 27 2026

...Washington Cascades & Olympics... Days 1-2...

A strong and meandering closed upper low in the Gulf of Alaska
will direct a storm system forming on its southern flank at British
Columbia the first half of the week. With the Gulf of Alaska low
slow to move east and low level ridging in place off the southern
CA coast, low- level SWrly flow will supply a narrow corridor of
Pacific moisture into the Pacific Northwest today and into Wednesday.
Snow levels will generally reside above 3,000ft today, but a cold
frontal passage and falling 700-500mb heights Tuesday night will
cause snow levels to dip to as low as 2,000ft by Wednesday. Still,
the cold air in wake of the cold frontal passage is not
particularly cold, and the best moisture advection will have
already concluded by Wednesday. This is likely to cause periods of
mountain snow on Wednesday in the Olympics and Cascades to as low
as 2,000ft, but rates will not be overly heavy even through
Wednesday night.

WPC probabilities for >4" of snow are high (>70%) for elevations
above 4,000ft north of I-90. Stevens Pass sports high chances
(>70%) for snowfall totals >4" through Wednesday night, while
Snoqualmie Pass has moderate chances (50-70%). Stevens Pass poses
the slightly better odds for snowfall totals >8", ranging between
30-50%. Some locally hazardous travel conditions are possible at
pass level, but the heavier totals surpassing 8" will likely be
found at higher and more remote elevations.

...Northern Maine... Days 2-3...

Starting Wednesday night, sheared lobes of 500mb vorticity racing
over the northern Great Lakes will generate PVA over northern New
England at the same time that low-level SWrly flow results in low-
level WAA and increased moisture content. Weak high pressure over
Quebec and sufficiently cold enough air over Maine will support
periods of snow over northern Maine with some minor icing possible
in central ME. As the first disturbance races east, a second 500mb
shortwave trough will spawn a second low over the northern Mid-
Atlantic Thursday evening. Periods of snow may envelope northern
Maine Thursday night as a cold front races south and forces
boundary layer temperatures to crash below freezing. There remains
some model spread in solutions regarding this second round of snow
Thursday night, so confidence in the snowfall placement and amounts
for the second round of snow is lower. At the moment, 48-hour WPC
probabilities show low chances (10-30%) for snowfall totals >4"
along the ME/Quebec border.


The chances for significant ice across the CONUS is less than
10 percent.


Mullinax

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