High Wind in Montana, January 17 to 20, 2021

Area Forecast Discussion
National Weather Service Great Falls MT
1055 AM MST Sun Jan 17 2021

...AVIATION SECTION UPDATED...

.SYNOPSIS...
A weather disturbance will move southeastward through the region
today and tomorrow. As a result, expect mostly mountain snow to
develop this morning, and then continue into Monday. The snowfall
will be heaviest in the Kings Hill and Big Sky regions. Drier
conditions move into the region for the middle portion of the
week, but colder temperatures and snow are expected by next
weekend.

&&

.UPDATE...

The morning update has been published. Not much change was needed
to the previous package but did freshen pops, winds and temps toward
current trends. Shortwave trough and cold front will continue to
approach from the northwest. Snow is already falling over some of
the mountain passes this morning with the first wave of moisture.
This activity will increase this afternoon as the northwesterly flow
becomes more unstable from H700 cold air advection. All winter
weather products are handling the current situation well so no
changes were needed for those headlines. RCG

&&

.AVIATION...
1055 AM MST Sun Jan 17 2021 (17/18Z TAF period)

Mountain snow will continue to increase this afternoon as a
shortwave trough approaches from the northwest. Brief rain/snow
showers may impact lower elevations for the remainder of this
afternoon, with more prolonged periods of MVFR/IFR conditions, due
to snow, possible tonight into Monday morning for KCTB, KHVR, KLWT,
and KBZN. Gusty west winds are expected ahead of the disturbance
will shift more northwesterly this afternoon for most locations.
Mountains/passes will be obscured until Monday evening, when
conditions begin to improve across the region. RCG

Refer to weather.gov/zlc for more detailed regional aviation weather
and hazard information.

&&

.HYDROLOGY...
400 AM MST Sun Jan 17 2021

The flood advisory continues for the Jefferson River near Three
Forks until further notice.

The river gauge reading there continues to hover around minor
flood stage, with little variation over the last 24 hours.

Although no reports of flooding have been received so far, the
current forecast indicates that the river level should remain near
flood stage for the time being. Any impacts from this ice jam
should be minor and along the river bank.

&&

.PREV DISCUSSION...
/ISSUED 520 AM MST Sun Jan 17 2021/
520 AM Update...Added the Rocky Mountain Front to the winter weather
advisory until 5 PM Today.

Today thru Monday...An upper level disturbance/combined with a
Pacific front is expected to move southeastward through the region
today. Gusty west winds are expected ahead of the front,
especially over the Northern Rockies/Cut Bank area today. Snow
develops this morning along the divide and across Central MT. The
snowfall could become heavy at times tonight at higher elevations
over Central MT and in the Big Sky area. Overall, just minor
adjustments to the total snowfall expected from today thru Monday,
thus the winter weather advisory will continue. Temperatures will
be mild today ahead of the front, with slightly cooler
temperatures expected on Monday. Most of the snow diminishes over
our region by Monday evening.

Tuesday through Thursday...There is the potential for a short
period of strong winds Tuesday evening into early Wednesday
morning over the Northern Rockies and in the Cut Bank area. A
high wind watch might be needed for this region. Otherwise, expect
slightly above normal temperatures for Tue/Wed...with colder air
starting to move into the region on Thursday. Snowfall chances
have decreased during this period compared to what the forecast
had a few days ago, thus now only a passing snow shower is
possible.

Friday thru Sunday...Generally below normal temperatures are
expected by next weekend, as an upper level trof swings through
the region. Some very cold air in southern Canada will try to move
southwestward into the Havre area...the question is how far
though? Thus expect adjustment to temperatures in this region over
the next few days. Also the GFS is more aggressive with snowfall
next weekend along the cold air boundary than the EC model is.
Thus increased NBM pops a bit, but overall, quite a bit of
uncertainty in the forecast for next weekend in terms of
where/when/how much snowfall might fall. Brusda

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  48  29  39  21 /  20  50  40  10
CTB  43  29  38  20 /  20  30  30  10
HLN  45  31  38  18 /  30  30  30  20
BZN  40  22  36  13 /  40  60  50  20
WYS  29   6  26  -4 /  70  60  40  10
DLN  42  20  34  11 /  20  20  20  10
HVR  44  28  39  21 /  50  50  20  10
LWT  43  26  33  18 /  70  70  50  20

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 5 PM MST this afternoon Northern
Rocky Mountain Front...Southern Rocky Mountain Front.

Winter Weather Advisory from noon today to 9 PM MST Monday above
4000 feet for Cascade...Fergus...Judith Basin...Meagher.

Winter Weather Advisory from noon today to noon MST Monday
Gallatin.

Winter Weather Advisory from noon today to noon MST Monday above
5000 feet for Central and Southern Lewis and Clark...Jefferson.

&&

http://www.weather.gov/greatfalls