High Wind in Montana, December 20, 2016

Area Forecast Discussion
National Weather Service Great Falls MT
303 PM MST Tue Dec 20 2016

.DISCUSSION...

Today through Thursday...Snow continues over the Rocky Mountains
and most of the Southwest MT ranges amid a moist westerly flow.
Water vapor imagery and surface observations reveal a potent
shortwave system over the southern Canadian Rockies, with lee
side pressure falls over souther Alberta. The trailing surface
front is moving through northern Idaho, and will be expected to
emerge across the Rockies around 00Z this evening. Winds have been
gradually strengthening today, but so far have remained below high
wind criteria. However, the Alberta clipper system is forecast to
intensify and strengthen the pressure gradient. Winds are forecast
to increase near high wind criteria for a short time as the front
moves across North-central MT from west to east this evening.
Therefore, a high wind warning remains in effect starting at 4pm
MST and continue through midnight. Conditions improve overnight,
with very light orographic snow continuing in NW flow through
Wednesday morning. Skies clear Wednesday and Thursday as dry air
moves across the region. Breezy conditions continue with the
strong westerly flow aloft. PN

Thursday Night through Tuesday...This period continues to be marked
by forecast model uncertainty for a strong Pacific shortwave trof
coming into the West Coast late Fri. A consensus-type forecast of
the varying model solutions indicates the leading edge of
precipitation from this system should reach our region starting Sat
morning and followed by the primary moisture plume Sat night through
most of Sunday. That translates into a fairly steady period of light
snow through the Christmas holiday weekend, with most locations
receiving a few inches of accumulation before the system heads into
the Upper Midwest states on Sun night.  Expect mostly dry conditions
on Mon and Tues, but our brief run of above-freezing temps comes to
an end with the Christmas system, as a colder Canadian airmass
settles into the state as the shortwave exits. High temps drop
back to 20s on Sat and re

&&

.AVIATION...
/Updated 1740Z/

Strong and fast moving Alberta Clipper will sweep through the
forecast area between 00Z and 06Z Wednesday. Mid- and high-level
clouds along with scattered rain/snow showers are expected ahead of
the system for areas IFR/MVFR conditions and mountain obscurations
over the western and Southwest Montana mountains. Strong winds,
mountain wave activity and clear air turbulence should be
anticipated downwind of the Continental Divide with very strong
winds likely to last 4 to 6 hours after surface front passage.
Clearing skies and diminishing winds will move into the region after
09Z. mpj

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  23  32  21  34 /  30   0   0   0
CTB  22  32  17  33 /  20   0   0   0
HLN  17  31   8  30 /  50  10   0   0
BZN  12  28   6  29 /  40  10   0   0
WEY  -5  21 -12  21 /  90  30   0   0
DLN   8  26   4  26 /  50  10   0   0
HVR  19  32  19  36 /  10  10   0   0
LWT  19  30  17  35 /  20  10   0   0

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
High Wind Warning until midnight MST tonight Cascade...
Chouteau...Eastern Glacier...Eastern Pondera...Eastern Teton...
Judith Basin...Liberty...Toole.

Winter Weather Advisory until 11 PM MST this evening
Beaverhead...Central and Southern Lewis and Clark...Gallatin...
Jefferson...Madison...Southern Rocky Mountain Front.

Winter Storm Warning until 11 PM MST this evening above 5000
feet for Northern Rocky Mountain Front.

Winter Weather Advisory until 11 PM MST this evening below 5000
feet for Northern Rocky Mountain Front.

&&

weather.gov/greatfalls