FOUS11 KWBC 310706
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
306 AM EDT Fri Oct 31 2025

Valid 12Z Fri Oct 31 2025 - 12Z Mon Nov 03 2025

...Northern Appalachians...
Day 1...

The powerful storm system tracking over Quebec will generate
strong CAA at low-levels at the same time as a TROWAL pivots over
the Northern Appalachians. The depth of the atmosphere is
sufficiently saturated and cold enough to support periods of snow
at elevations above 1,500ft in the Adirondacks and above 2,000ft in
the Green and White Mountains. NWrly flow will support enhanced
upslope flow into some of the orographically favored mountain
ranges, thus aiding in more efficient dynamic cooling aloft. The
lowest 1,000ft of the boundary layer are likely to hover around or
slightly above 32F, which will make snow tough to accumulate during
the day on Friday. But as the sun sets, snow falling within a
marginaly-cold boundary layer should improve the chances for snow
to accumulate in the higher elevations. WPC probabilities do show
some low-to-moderate chances (10-40%) for snowfall totals >2" in
the Adirondacks, but probabilities for >4" of snowfall are topping
out around 10%. The WSSI does depict splotchy areas of Minor
Impacts (winter driving conditions, use caution while driving) in
the Adirondacks, Green, and White Mountains. One location that
could see locally heavy snowfall is Mount Washington where the
combination of strong winds and snowfall totals approaching 6"
could support Moderate Impacts.

...Washington Cascades...
Days 2-3...

A shortwave disturbance at the base of a massive longwave trough
positioned over the northeast Pacific will direct a highly
anomalous IVT topping 1,000 kg/m/s at the Pacific Northwest Friday
night and into Saturday. There is no shortage of moisture within
the IVT as PWs approach 1.25" over western WA, which in some
instances tops the 99th climatological percentile per ECMWF and
NAEFS SATs. That said, the Pacific air-mass is also rather mild and
antecedent boundary layer temperatures are not cold enough to
support heavy snowfall below 5,000ft south of US Route 2. Most
passes should remain below the freezing level, making rain the
primary precipitation type below 5,000ft. One exception may be
Stevens Pass, where some light snowfall totals are possible. The
Cascades north of US-2 above 5,000ft maintain better odds for
locally heavy snowfall, where 50-80% probabilities of exceeding 4
inches are depicted.


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

Mullinax
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