179
FOUS11 KWBC 281750
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
150 PM EDT Wed Oct 28 2026

Valid 00Z Thu Oct 29 2026 - 00Z Sun Nov 01 2026


...Northern Cascades and Northern Rockies...
Days 1-2...

Closed mid-level low will spin just offshore the WA coast into
Friday, with modest downstream divergence and shedding spokes of
vorticity driving ascent into the Pacific and Interior Northwest
from the Olympics through the Northern Rockies. Although moisture
will spread eastward within pinched flow SE of this mid-level
feature, PWs will be generally near normal, and the most intense
ascent (through synoptic forcing and upslope enhancement) will be
waning early D1, so total additional snowfall is likely to be
modest. Waves of precipitation falling as snow above generally 4000
ft will continue into at least Friday, but with intensity waning
outside of pockets of convectively-enhanced precipitation driven by
mid-level instability and steepening lapse rates beneath the upper
low. Still, additional snowfall is likely to be modest, as
reflected by just small pockets of 50%+ probabilities of 4 inches
or more in the highest Olympics, northern Cascades, and Northern
Rockies in the vicinity of Glacier NP.


...Sierra into the Four Corners...
Day 3...

Although most of the winter precipitation associated with the next
system will occur beyond this current forecast period (mostly D4+),
some high-elevation snow will spread across the Sierra and into the
San Juans above 9000 ft before 00Z Sunday. This will be associated
with an impressive wave of low pressure lifting northeast from the
eastern Pacific with anomalous PW/IVT surging into the Southwest.
While snowfall D3 will likely be minimal, the extremely moist
column will support anomalously low SLR with a 10-30% chance of at
least minor impacts due to snow load developing before expanding
into D4.


The probability of significant ice across the CONUS is less than
10 percent.


Weiss


$$