FOUS11 KWBC 261927
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
327 PM EDT Sat Oct 26 2024

Valid 00Z Sun Oct 27 2024 - 00Z Wed Oct 30 2024


...Pacific Northwest to the central Rockies...
Days 1-3...

A deep upper/sfc low south of the Gulf of Alaska and west of
British Columbia will push eastward over the next couple of days,
with its attendant cold front moving into/through the PacNW. A
series of mid-level vort maxes in the mid-levels will bring rounds
of precipitation to the region, progressively pushing southeastward
into Monday/Tuesday, as colder air filters in behind the front.
High snow levels (7000-8000ft) tonight will lower to around
4500-5000ft Sunday evening into early Monday from northwest to
southeast across the WA/OR Cascades. D1 probabilities of at least 8
inches of snow are highest above 7000ft with any significant snow
above the passes but some accumulation is likely at the higher
passes (e.g., White and Washington Pass).

For Mon-Tue, the trough axis will move ashore with streams of
vorticity strung out over much of the West. Snow levels will
continue to fall from northwest to southeast to around 4500-6000ft
(north to south) with broad SW flow aloft and W to NW flow at the
surface. Though the initial moisture plume will be around the 90th
percentile into WA/OR D1, it will weaken as the system progresses
inland which should result in a broader area of light to moderate
QPF and snow at lowering elevations from NV/UT across ID/WY.
Orographic enhancement on the southwest side of the terrain will
increase amounts somewhat, including over central Idaho and
especially around Yellowstone into the Absarokas, Wind River, and
eventually the Bighorns. Here, WPC probabilities for at least 8
inches of snow are >50% above 9000-10,000ft.

Farther south, generally lighter snow is expected for the Sierra
and into the Wasatch/Uintas where some 6"+ amounts are possible
above 8000ft. SW flow will also favor the San Juan Mountains in SW
CO by late Mon into Tue where WPC probabilities for at least 8
inches of snow are >50% above 11,000ft.

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

Fracasso








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