High Wind and Strong Wind in Montana, November 15 to 16, 2021

Area Forecast Discussion
National Weather Service Missoula MT
247 PM MST Mon Nov 15 2021

...DAMAGING WINDS PRESENT ACROSS NORTHERN ROCKIES THIS EVENING
THROUGH TUESDAY MORNING...

.DISCUSSION...

A powerful Pacific jet stream is expected to move over the Northern
Rockies this evening through Tuesday morning, bringing damaging
winds down to the deck. The strong winds will be accompanied by
strong mountain wave activity, where winds off the terrain
concentrate over a limited area for a short duration. High-profile
vehicles will be particularly susceptible to dangerous crosswinds.
Recent saturated ground and wind gusts over 60 mph may damage trees
and infrastructure.

A cold front associated with the powerful Pacific jet stream will
move across the Northern Rockies overnight tonight, concentrating a
burst of snow and rain along the front. There may be a quick dusting
of snow and a brief period low visibility as the front passes
tonight.

By Tuesday afternoon, air aloft is anticipated to cool significantly
and create a potential heavy snow scenario in deep instability.
Portions of west central and southwest Montana will be prime for
snow squalls Tuesday afternoon and evening. Travelers should prepare
for short-duration, powerful bursts of snow that will reduce
visibility and create dangerous road conditions. Snow is anticipated
to drift across the Continental Divide sometime after midnight
(Tuesday into Wednesday) and dwindle throughout the remainder of the
overnight.

High pressure will be present over the Northern Rockies Wednesday
and Thursday, however the nature of the air in-place will not be
supportive to warm conditions. In fact, some valleys may not warm
nearly as much as surrounding terrain (i.e., temperature
inversions), but the magnitude of this valley cold will be somewhat
dependent upon whether or not Tuesday evening snow remains on the
ground in the Tuesday-Wednesday timeframe.

A Pacific storm system is anticipated to disrupt the high pressure
in the Friday through Saturday period, with high-elevation snow and
a wintry mix at lower elevations. The northwest oriented airflow at
the ridgetops on Saturday may be conducive for another round of
banded snow feature, but current weather models provide only limited
clarity on that point.

Aside from a few weak storm system disrupting the status quo, high
pressure appears to be the most prominent weather feature present
across the Northern Rockies in the day 6-14 period. Valley cold
pools may become commonplace across the region, as sun angle
continues to drop.

&&

.AVIATION...Strong winds aloft will eventually mix down to the
surface and translate to widespread west-southwest winds of 20 to
30 knots with gusts up to 50 knots. Timing of strongest winds will
be around and after 16/0000Z through 16/1500Z, with elevated
winds persisting through 17/0000Z. Pilots should also anticipate
low level wind shear at all terminals through roughly 16/1200Z.
Precipitation will begin as rainfall for most locations this
evening with a transition to snow by Tuesday morning. Snow squalls
with isolated wind gusts and periodically low visibility in areas
of heavier bursts of snow will be possible across western
Montana, primarily impacting KMSO and KBTM.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...     High Wind Warning from 7 PM this evening to 8 AM MST Tuesday
     Missoula/Bitterroot Valleys.

     High Wind Warning until 2 AM MST Tuesday Flathead/Mission
     Valleys...Kootenai/Cabinet Region...Lower Clark Fork Region.

     High Wind Warning until 8 AM MST Tuesday West Glacier Region.

     High Wind Warning from 7 PM this evening to 8 AM MST Tuesday
     Bitterroot/Sapphire Mountains...Butte/Blackfoot Region...
     Potomac/Seeley Lake Region.

ID...Wind Advisory until midnight PST tonight Northern Clearwater
     Mountains...Southern Clearwater Mountains.

&&