072
FXUS65 KTFX 041737
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1037 AM MST Thu Dec 4 2025

Aviation Section Updated.

.KEY MESSAGES...

 - Snow begins across some of the higher terrain as the first in
   a parade of winter storms begins to move into the area.
 - Snow becomes more widespread Friday and Saturday, with
   heaviest snowfall over the higher terrain but still some
   accumulating snow on the plains.
 - Active weather pattern continues next week with near daily
   chances for rain and/or snow.

&&

.DISCUSSION...
/Issued 441 AM MST Thu Dec 4 2025/

 - Meteorological Overview:

After a 24 hour period of quieter weather, our weather will turn
more active once again this afternoon as an upper level jet streak
sets up just to our south as moisture surges in ahead of an
approaching trough, which will produce snowfall over the Mountains
of Central and Southern Montana this afternoon and overnight
tonight. Elsewhere, today will generally be a cloudy day across
North Central and Southwestern Montana with a few light snow
showers or flurries and some gusty winds across the plains thanks
to a building pressure gradient between high pressure west of the
divide and a developing lee trough over the plains.

Snowfall over the higher terrain will temporarily taper off
across the higher terrain after sunrise tomorrow as the jet streak
moves east. During the day, expect cloudy skies with a few light
snow showers across the entire area, with snow becoming more
widespread during the late afternoon hours as our next system
pushes into the area. Snowfall will quickly become more widespread
after sunset as this system approaches, with impressive snowfall
rates over the higher terrain (1-2 inches an hour at times) and
generally lighter snow on the plains and valleys. Snow will taper
off a bit over the course of the day and generally end across the
area by late Saturday evening. Accumulations in excess of a foot
between these two systems will be common at and above pass level,
which will make travel over the passes difficult to near
impossible at times, and while the valleys of southwestern Montana
may wind up with generally less than an inch or two, there is a
chance for a band to set up across the plains late Friday night or
Saturday that could result in some localized amounts over 4
inches, mostly north of a Cut Bank to Lewistown line.

Looking into next week, Sunday will see most areas clear the
snow, save for some light leftover snowfall across the Rocky
Mountain Front and in the Greater Yellowstone area. However, the
parade of storms will continue next week, with near daily chances
for at least some mountain snow and lower elevation rain and/or
snow through much of next week. Ludwig

 - Forecast Confidence & Scenarios:

Lower Elevation Snow Thursday through Saturday:

Light lower elevation snow is possible with the Thursday shortwave
but the main event for lower elevations will be Friday afternoon
through Saturday afternoon with the arrival of the second
shortwave. With the second system, a widespread 1-2 inches is
possible across a good portion of north-central Montana except the
Golden Triangle which is set to miss most of the snowfall with
this event. As of right now, there are a couple areas along the
lower elevations which would be candidates for higher snowfall
amounts, particularly along and north of the Highway 200 corridor
between Great Falls and Lewistown, the Smith River Valley, and
the Gallatin Valley. Confidence was not high enough to add them to
the initial Winter Storm Watch at this time. However, confidence
is slowly increasing for at least some impacts, which may
eventually result in at least a Winter Weather Advisory.


Heavy Mountain Snow Thursday through Saturday:

Confidence in a highly impactful winter storm continues to
increase over the higher terrain of North Central, Central, and
Southwestern Montana this morning. A first round of snowfall is
expected to begin this afternoon across the mountain ranges east
of Interstate 15, which is expected (80% confidence) to produce
enough impacts to justify upgrading these zones to a Winter Storm
Warning and bringing up the start time to 11am this morning. Snow
will peak in intensity across these mountains overnight tonight,
with snowfall rates of 1/2 - 1 inch per hour at times. Snowfall
will taper off a bit early tomorrow morning, but at least some
light snowfall is likely to continue through the day across the
higher terrain before picking back up Friday evening as the second
half of this system pushes into the area. Snowfall rates at and
above pass level with this second round are likely to exceed 1
inch per hour at times, particularly over King`s Hill Pass, which
will make travel quite difficult before and even after snowfall
tapers off late Saturday afternoon or evening. Snowfall totals
across the higher terrain are likely to be in excess of a foot to
18 inches across some of the higher passes by the time this system
exits the area.


Travel Impacts Thursday through Saturday:

By far, one of the biggest concerns with this system will be the
timing and how it impacts the Thursday evening, Friday morning,
and Friday evening commutes. With the initial snowfall on
Thursday, depending on road temperatures, there will likely be
some initial melting of the first few flakes. When this moisture
refreezes as the night goes on the concern will be patches of ice
forming and then receiving more snow as the event continues
creating very slick roads. Additionally, some periods of moderate
to heavy snowfall are possible particularly with the initial push
on Thursday evening and again with the arrival of the second
shortwave on Friday afternoon/evening. This could lead to periods
of reduced visibility which will add to the potential for
hazardous driving conditions.

In particular, there is great concern regarding the impacts
possible along I-90 from Belgrade to Bozeman Pass. Snowfall
probabilities in Bozeman proper were not enough to warrant
including Gallatin Valley in the Winter Storm Watch but minor to
moderate impacts are still possible in the area due to slick roads
and brief periods of moderate to heavy snowfall, particularly on
the far eastern side of the Gallatin Valley heading towards the
pass.

Additional mountain passes and roads that might experience
significant impacts include, but are not limited to, Marias Pass,
Kings Hill Pass, Deep Creek Pass, and Highway 191 south of Bozeman
to the Idaho border. If heading out, motorists need to be prepared
for rapidly changing and deteriorating road and weather
conditions and it is advised to carry chains as well as an
emergency kit. -thor/Ludwig

&&

.AVIATION...
04/18Z TAF Period

Snow will affect most of the terminals during at least a portion of
this TAF Period. Snow will reduce visibility and ceilings down to
at least MVFR levels at the KBZN, KEKS, and KHLN terminals during
this TAF Period. At the KGTF and KLWT terminals there is at least
a 15% chance for snow during the duration of this TAF Period.
There will be mountain obscuration across most of North-central,
Central, and Southwestern Montana during the duration of this TAF
Period. Between now and 05/06Z there will be isolated instances of
low-level wind shear across North-central, Central, and Southwestern
Montana. -IG

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  38  23  36  16 /  40  30  60  80
CTB  35  16  29   4 /  20  10  40  70
HLN  36  25  37  24 /  60  80  80  90
BZN  33  24  35  25 /  70  80  70  90
WYS  24  14  29  18 /  90  90  90 100
DLN  35  22  38  27 /  30  60  50  70
HVR  35  18  29   5 /  30  30  40  90
LWT  36  22  34  13 /  40  40  40  90

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Winter Storm Watch from late tonight through Saturday afternoon
for East Glacier Park Region-Northwest Beaverhead County-
Southern Rocky Mountain Front.

Winter Storm Warning until 2 PM MST Saturday for Big Belt,
Bridger and Castle Mountains-Gallatin and Madison County
Mountains and Centennial Mountains-Little Belt and Highwood
Mountains.

&&

$$
http://www.weather.gov/greatfalls