FOUS11 KWBC 282006
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
406 PM EDT Mon Oct 28 2024

Valid 00Z Tue Oct 29 2024 - 00Z Fri Nov 01 2024


...Rockies onto High Plains....
Days 1-2...

A slightly positively-tilted upper trough over the length of the
Cascades this afternoon shifts east north-central Rockies through
Tuesday as the leading SWly jet tracking up the High Plains becomes
dominant. A well-defined shortwave trough leads the main trough and
lifts northeast AZ to southeast WY Tuesday. Strong warm air
advection ahead of this wave makes for high elevation snow over CO
tonight into Tuesday with Day 1 snow probs for >6" high above the
10,000ft snow level including the San Juans and Sawatch.

Strong mid/upper level forcing with this leading trough combines
with low level upslope flow on the northwest side to support
periods of heavy snowfall along the favored terrain over much of
the Utah terrain tonight into Tuesday with Day 1 snow probs for
>6" high over the Tushar/Wasatch/Uinta. Then much of Tuesday
includes heavy snow over WY terrain including the Wind River,
southern Absaroka, and Bighorns. Day 1.5 snow probs for >8" are
50-80% across this terrain where snow levels will be around 5000ft
which will impact many of the mountain passes in WY.

Lee-side sfc cyclogenesis over eastern CO begins Tuesday
which helps enhance banding/cooling Tuesday afternoon over
northeastern WY and western SD including the Black Hills. A
deformation axis of precip then extends northeast across ND into
northern MN Tuesday night. There is uncertainty with the intensity
and thermal aspects of this banding. For now, the greatest snow
banding potential is afternoon between the Black Hills and Bighorns
where Day 1.5 snow probs for >4" are 40-70%. Moderate snow
potentially shifts over the southeast corner of MT and
northwestern SD Tuesday evening, though little guidance supports
banding strong enough to overcome the weak thermals to produce
accumulating snow there.


...Northwest...
Days 2/3...

A rapidly developing low crosses the Gulf of Alaska Tuesday with
the base of trough rounding the low crossing the PacNW coast
Wednesday afternoon. The high moisture plume on southwesterly flow
ahead of the trough brings snow levels up to 4000-5000ft on the
Cascades Wednesday afternoon, then height falls with the trough and
likely low center Wednesday night bring snow levels below 4000ft
where they stay through Thursday. Snow probs for >6" are 50-90%
over the OR Cascades on Day 3 where more than a foot is likely
through the storm which continues into Friday.


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


Jackson


$$

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