223
FXUS65 KTFX 201110
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
410 AM MST Thu Nov 20 2025

Aviation Section Updated.

.KEY MESSAGES...

- After some patchy morning fog, drier and mild conditions return
  by this afternoon.

- Breezy to windy conditions heading into the weekend, strongest
  along the Rocky Mountain Front where gusts will exceed 60 mph
  at times.

- A strong cold front will bring windy conditions Monday
  into Tuesday with accumulating snow along the Rocky Mountain
  Front.

- Colder temperatures and periods of light snow are expected
  heading into Thanksgiving.

&&

.DISCUSSION...
/Issued 319 AM MST Thu Nov 20 2025/

 - Meteorological Overview:

Weak ridging is developing over the Northern Rockies while a
closed low slides down the Pacific coast and eventually merges
with another trough over the Great Basin and southwestern US.
While moisture has thinned in the upper levels, the boundary layer
remains moist and has maintained considerable low stratus and
patchy fog, mostly over central and southwest MT. The latest hires
guidance highlights patchy fog persisting over the golden
triangle area through mid- to late morning and there may be some
sunrise surprise fog in the southwest as well. An expanding
stratus deck over the southern two thirds of the CWA should
preclude widespread dense fog impacts.

Once the fog clears out, milder and drier conditions will move in
for the remainder of today. Some fog redevelopment can`t be ruled
out again tonight, but southwesterly breezes will start to
increase and limit the fog opportunities to the more susceptible
river/wind protected valleys. Westerly flow increases over the
Northern Rockies this weekend and brings periods breezy to windy
conditions and some mountain snow, mostly along the Rocky Mountain
Front. A strong trough and attendant cold front surges through
the state Monday into Tuesday and ushers in a cold northwesterly
flow aloft for the remainder of the week. This looks to result in
a period of windy conditions followed by occasional mostly light
snow and the coldest temperatures of the season so far. - RCG

 - Forecast Confidence & Scenarios:

Increasing winds and light Rocky Mountain Front snow this
weekend...

A tightening surface pressure gradient will bring an initial wave
of windy conditions to the Rocky Mountain Front Friday into
Saturday. Probabilities for 55 mph/75 mph + gusts increase to
around 80%/40% respectively over the eastern foothills of the
Rocky Mountain Front eastward to the Browning area. The
probability for 55 mph gusts falls to around 40% in the Cut Bank
area. Despite a tightening surface pressure gradient, H700 winds
will mostly be less than 50 kts and will have a northwesterly
trajectory. Given the lower probabilities and lack of upper level
wind support, I continued to hold off on issuing any high wind
products for the time being. Winds will also be on the increase in
other areas throughout the weekend with many central and north-
central locations seeing gusts in the 30 to 50 mph range. Mountain
snow looks to be on the lighter side and mostly confined to the
higher terrain of the Rocky Mountain Front.

Colder pattern shift heading into Thanksgiving...

Ensembles are still highlighting a strong trough and attendant
cold front to surge through the Northern Rockies sometime Monday
into Tuesday. The dynamics still look supportive for a period of
strong, gusty winds, but have backed off a bit over the last 24
hours. The NBM probabilistic guidance has increased with all the
Rocky Mountain Front and portions of the plains now seeing over a
50% chance for 55 mph + gusts. Since the ECMWF ensemble suite was
less enthusiastic for this event, the Extreme Forecast Index and
Shift of Tails has also shown a weaker signal for anomalous winds.
The timing of the front will play a significant role in whether
the strongest 40 to 60 kt H700 winds transfer to the surface.

This front will usher in a more active and colder pattern, though
recent ensembles continue to decrease the amplitude of the
troughs passing through the Northern Rockies and even delay the
coldest air from arriving until after Thanksgiving. Overall, this
will still deliver the coldest temperatures of the season so far,
especially with how warm it has been lately. As far as snow goes,
the Rocky Mountain Front looks to to be the winner for
accumulating snow Monday afternoon through early Tuesday when
there is around a 50% chance for 6 inches of snow or more at
Marias Pass. - RCG

&&

.AVIATION...
20/12Z TAF Period

Primary concern through 20/18Z will be patchy fog and or low
stratus clouds. IFR/LIFR fog and clouds will be most prevalent
near KCTB and KGTF while the southwest terminals (KBZN, KEKS, and
KHLN) mostly observe MVFR stratus clouds. Partial to full clearing
takes place after 20/18Z. The HREF ensemble highlights a 30%
chance for fog redevelopment after 21/00Z along the Hi- Line (KCTB
and KHVR), but increasing southwesterly breezes should preclude
widespread development. - RCG

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  52  32  52  36 /   0   0   0   0
CTB  48  29  48  33 /   0   0   0   0
HLN  49  28  49  29 /   0   0   0   0
BZN  49  24  50  24 /   0   0   0   0
WYS  44  18  44  21 /  10   0   0   0
DLN  47  24  48  24 /   0   0   0   0
HVR  44  25  51  29 /   0   0   0   0
LWT  52  29  54  30 /   0   0   0   0

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
None.
&&

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