High Wind in Montana, December 2 to 3, 2019

Area Forecast Discussion
National Weather Service Great Falls MT
235 AM MST Mon Dec 2 2019

.SYNOPSIS...

Gusty southwest winds will continue to affect much of north-central
MT through Tuesday with strongest winds and widespread blowing and
drifting snow occurring along and just east of the Rocky Mountain
Front. Aside from some mountain snow showers, generally dry
conditions will prevail with temperatures trending above seasonal
averages through the first half of the week.

&&

.DISCUSSION...

Today through Tuesday...

Weak upper level ridge that developed over the region is breaking
down as several smaller scale weather disturbances move across the
region in a westerly flow aloft through Tuesday. Plume of moisture
from the Pacific continues to sag south across SW MT today, keeping
a chance for some snow showers in the West yellowstone to Big Sky
areas as well as along the continental divide west of the Rocky Mtn
Front, while mainly dry conditions prevail elsewhere. Windy
conditions will persist across most of north-central MT through
Tuesday with a strong pressure gradient continuing along the east
slopes of the Rockies but flow aloft looks to peak today with
strongest gusts likely this afternoon along and east of the Rocky
Mtn Front. Significant blowing and drifting of snow is expected to
continue along the Rocky Mountain Front and Glacier county areas
today where winter weather highlights will continue with Blizzard
conditions most likely in areas areas along the immediate east
slopes of the northern Rocky Mtn Front. Will let the winter weather
advisories for blowing snow expire for areas further east across
central MT this morning as it remains windy with likely some
drifting snow in exposed areas, but temperatures here have largely
risen above freezing, and this combined with compaction and scouring
of the snowpack over the last 24 hrs should limit raising the snow
to reduce visibility. The duration of the winter weather highlights
for the Rocky Mtn front and Glacier county will need to be re-
evaluated later today as scouring, compaction and warmer
temperatures begin to mitigate blowing snow potential there as well,
especially after winds peak this afternoon. Hoenisch

Tuesday Night through next Monday...

The progressive pattern with a brisk westerly flow aloft is still on
track through Friday, which should keep the area generally dry and
mild with breezy westerly winds. However, some precipitation is
possible in the mountains of North Central Montana at times. A weak
disturbance in the flow with an associated Canadian cold front will
also bring a quick shot of slightly below normal temperatures on
Thursday, but temperatures should warm back above normal on Friday.

The weather pattern will then become cooler and more unsettled for
the weekend into early next week. A low pressure trough will move
into the Pacific Coast states on Saturday, and the resulting
southwest flow aloft will tap into Pacific moisture and bring a good
chance of precipitation to the mountains of Western and Southwest
Montana. However, breezy southwest downslope winds will likely keep
lower elevations dry with continued mild temperatures. Forecast
models have now come into better agreement for Sunday into Monday in
having this trough merge with the Hudson Bay Low in Canada to
develop a large and broad low pressure trough over North America.
This puts Montana under a northwest flow aloft that will cool
temperatures back below normal; just how cold temperatures could
reach is a bit uncertain at this time. A disturbance in the flow
will also bring a good chance of precipitation to the area on
Sunday, but it will likely move out of the area on Monday. This does
not appear to be a significant winter system at this time, but we
will continue to monitor it for potential winter highlights.
Coulston

&&

.AVIATION...
Updated 1040 PM MST Sun Dec 01 2019 (02/06Z TAF Period)

A weak disturbance moving through westerly flow aloft will bring
some broken mid to higher level cloudiness to the region through
the rest of tonight. Best chance for snow showers and local MVFR
conditions is across SW MT with a few showers also possible
further north in the KLWT and KHVR areas. Gusty SW winds persist
along the east slopes of the Rockies and increase further late
tonight through Monday morning with some potential for visibility
reduction in times at KCTB through Monday morning. Areas of low
level wind shear are expected at times in valley areas where winds
are lighter. Winds could also cause mountain wave activity with
turbulence aloft expected just downstream of the Continental
Divide. Hoenisch

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  40  31  42  30 /   0   0   0   0
CTB  37  29  40  32 /   0   0   0   0
HLN  40  27  42  23 /   0   0   0   0
BZN  38  21  39  17 /  10   0   0   0
WEY  30  15  31  15 /  60  10  10   0
DLN  35  19  36  17 /  10   0   0   0
HVR  38  25  39  27 /   0   0   0   0
LWT  40  27  42  26 /   0   0   0   0

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 6 AM MST Tuesday Eastern Glacier...
Southern Rocky Mountain Front.

Blizzard Warning until 6 AM MST Tuesday Northern Rocky Mountain
Front.

&&

http://www.weather.gov/greatfalls