FOUS11 KWBC 142025
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
325 PM EST Thu Nov 14 2024

Valid 00Z Fri Nov 15 2024 - 00Z Mon Nov 18 2024

...Western U.S....
Days 1-3...

A pair of Pacific storm systems will produce heavy mountain snow
from the West Coast to the Northern Rockies over the next few days.
Broad scale upper level ascent out ahead of a longwave trough off
the West Coast will also direct Pacific moisture at the Northwest
and northern California. Periods of snow will occur for many of the
Northwest U.S. mountain ranges which include (but are not limited
to) the Cascades, Siskiyou, northern Sierra Nevada, Blue, Sawtooth,
Bitterroots, Idaho Panhandle, and northern Montana Mountains). As
a potent upper level trough approaches California tonight (500mb
heights below the 2.5 climatological percentile via NAEFS), snow
levels will fall to as low as 4,000ft in the Sierra Nevada and as
low as 6,000ft in the San Gabriel and San Bernadino of southern
California. The heaviest snowfall will be mainly confined to
elevations at/above 6,000ft in the Sierra Nevada. By Friday
morning, the upper level trough will advance through the Great
Basin and into the Rockies by Friday night. Periods of snow will
move through northern Nevada and into the northern Rockies with the
Tetons, Wind River, and Absaroka ranges seeing the heaviest
snowfall Friday evening. Snow will also pick up in intensity along
the Wasatch, Uinta, and Big Horn ranges Friday night and into
Saturday morning. WPC PWPF shows moderate-high chances (50-70%) for
>4" of snowfall along the Sierra Nevada above 6,000ft, the
northern Great Basin above 6,000ft, and the Absaroka, Tetons, and
Wind River ranges above 8,000ft.

Meanwhile, the Pacific Northwest will see periods of light snow
this evening, with a fairly tranquil day weather-wise on tap for
Friday. By Saturday, the next Pacific trough approaches with a
stronger IVT (>500 kg/m/s, or above the 90th climatological
percentile via NAEFS) will direct another plume of Pacific moisture
at the region. Strong synoptic-scale support will also be present
as 200-500mb winds over western Washington top the 90th
climatological percentile. As the warm front arrives Saturday
night, snow levels will rise to as high as 5,500ft, but once the
cold front pushes through on Sunday, snow levels will crash and
result in precipitation changing over to heavy snow Sunday
afternoon in the Olympics and Cascades. Through 12Z Sunday, the
northern Cascades and the Idaho Panhandle above 5,000ft sport high
chances (>70%) for snowfall >6" with a low chance (10-30%) for >12"
in the tallest peaks of the northern Washington Cascades.

...Northern Maine...
Days 1-2...

An inverted trough revolving around the northern flank of a
retrograding storm system in the northwest Atlantic will direct a
stream of low-level moisture back west towards northern New England
late tonight into Friday. The air-mass over northern New England
(particularly Maine) will be sufficiently cold and dry enough for
wet-bulb temperatures within the boundary layer to remain below
freezing for at least a few hours. Strong easterly mid-level flow
with air-mass origins over the Atlantic will lead to warm-air
advection (WAA) that causes a >0C nose between 850-750mb Friday
morning. This setup will result in periods of sleet/freezing rain
over northern Maine and possibly into far northern New Hampshire.
WPC PWPF does depict some spotty areas with low chances (10-30%)
for ice accumulations >0.1" in portions of the North Woods and
Central Highlands of northern Maine. One notable location with
those potential ice accumulations includes Baxter State Park. These
icy conditions could result in Minor Impacts according to the
Probabilistic WSSI with low chances (10-30%) through Friday
afternoon. The primary impacts would be icy roads in some areas
that could lead to slick travel conditions.

Kebede/Mullinax


$$

= = =
To unsubscribe from WX-STORM and you already have a login, go to
https://lists.illinois.edu and use the "Unsubscribe" link.  Otherwise email
Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.20-Linux