Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
238 AM EST Thu Nov 16 2023

Valid 12Z Thu Nov 16 2023 - 12Z Sun Nov 19 2023

...Central Rockies...
Day 1...

Weak mid-level vort max coupled with the LFQ of an incoming 130+kt
jet will swing through UT into CO this morning and afternoon with
some high elevation snow over the Unitas into the CO Rockies,
generally above 9000ft, where WPC probabilities of at least 4
inches are at least 30% in the Park Range.


...The West...
Day 3...

The long-lived upper low off the CA coast will finally move inland
early Saturday in much weakened form, but its moisture plume
(precipitable water values +1 to +2 sigma) along with upper
diffluence an upslope flow will bring  periods of heavy snow at
elevations especially above 9,000ft. WPC probabilities show
low-moderate chances (30-50%) in the high Sierra. Farther north, a
sharp/strong shortwave in the northern stream will dive into the
Pacific Northwest, driving a strong cold front through the
Cascades. Snow levels there will drop from 6000-7000ft on Saturday
to below 4000-5000ft by the end of the period early Sunday,
bringing some snow to pass level. WPC probabilities of at least 4
inches of snow through 12Z Sunday are greater than 30% above about
4000-4500ft.

...Northern Maine...
Day 3...

A coastal low will race north NNEward Saturday afternoon into Nova
Scotia just ahead of a northern stream cold front that will bring
in marginally cold air to northern New England. Rain will change
to snow closer to the Canadian border but the brunt of the QPF
will lie well east. Trend has been for less QPF over the region as
the track stays offshore, but there remains a possibility of a
nudge westward as the low rapidly deepens to support a deformation
band on its northwest side Saturday evening over far northern
Maine. There, WPC probabilities of at least 4 inches are at least
30% but the spread in the models remains large at this time
(essentially 0-12" in the North Woods and 0-4" within about 50-75
miles of the Canadian border).

For Days 1-3, the probability of significant icing (at least
0.25") is less than 10 percent.

Fracasso