052
FXUS65 KTFX 211130
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
430 AM MST Fri Nov 21 2025

Aviation Section Updated.

.KEY MESSAGES...

 - Dense fog across portions of Southwest Montana will gradually
   dissipate through the late morning hours.

 - Strong and gusty winds will occur along the Rocky Mountain
   Front, especially west of the US Hwy 89 corridor north of
   Dupuyer.

 - A pattern change will occur early next week, with temperatures
   falling near to below normal and increasing chances for
   mountain snow.

&&

.DISCUSSION...
/Issued 251 AM MST Fri Nov 21 2025/

 - Meteorological Overview:

Zonal flow over the Northern Rockies through the weekend will help
to maintain above normal temperatures, breezy and gusty southwest to
west surface winds, and overall dry conditions. Winds will be the
strongest in the north-south orientated valleys of Southwest
Montana, Rocky Mountain Front, and the Montana Hwy 200 corridor from
Great Falls to Lewistown over this timeframe. Precipitation chances
will begin to increase along the Continental Divide north of the
Montana Hwy 200 corridor during the day on Sunday as Pacific
moisture advects eastward ahead of an approaching upper level
disturbance and cold front to begin the work week.

By Monday the aforementioned upper level disturbance and attendant
cold front will quickly slide east and over the Northern Rockies.
This disturbance will bring widespread gusty west winds to all of
Southwest through North Central Montana, especially along and
immediately behind the cold front. Temperatures will quickly drop in
wake of the cold front, with increasing chances for accumulating
snow to mainly the mountains, especially the Continental Divide and
Island Ranges of Central Montana. Northwest flow in wake of the
upper level disturbance will maintain chances for snow through the
remainder of the work week/Thanksgiving, most notably in northerly
upslope regions, and near to below normal temperatures. - Moldan

 - Forecast Confidence & Scenarios:

Dense Fog through this Morning...

Confidence is high that dense fog will persist across the Gallatin
Valley through 15-18z this morning, and for this reason a Dense Fog
Advisory has been issued until 17z in order to cover the entirety of
the Friday morning commute. Further west and north across the Helena
Valley, Meagher County Valleys, Elkhorn and Boulder Mountains,
Canyon Ferry Area, Missouri Headwaters, Madison River Valley, and
Beaverhead and Western Madison below 6000ft confidence in widespread
dense was too low for an advisory at this time; however, a Special
Weather Statement was issued to mention localized reductions in
visibility below 1/4 mile.

Strong Winds through this Afternoon...

Confidence is high that a strong pressure gradient, generally of
0.15mb/km to 0.2mb/km, orientated along the immediate Rock Mountain
Front from north of Gleason to the Canadian border will help to
support strong wind gusts in excess of 48kts for areas along and
west of the US Hwy 89 corridor. NBM4.3 probabilities for wind gusts
exceeding 48kts in the Cut Bank Area is around a 25% chance, with
the most likely window for these wind gusts occurring being between
12-18z. Further west for areas along and west of the US Hwy 89
corridor there is generally between a 25-55% chance for wind gusts
to reach 65kts per latest NBM4.3 guidance, with the strongest winds
occurring in the Dog Gun Lake area. While this event has the
potential for a couple of sites to meet High Wind criteria we will
address the strong winds with a Special Weather Statement for now
given the aforementioned probabilities; however, should wind speeds
and/or gusts approach High Wind criteria then a limited lead time
High Wind Warning may be needed.

High Wind Potential on Monday...

Climate anomaly indicators such as the NAEFS and ECMWF EFIs suggest
the potential, albeit limited, for a climatologically unusual period
of winds Monday morning/afternoon with the passage of an upper level
shortwave and cold front. H700 wind speeds per NAEFS analysis
support values approaching 50kts overspreading portions of Southwest
and North Central Montana between 12-18z, which are nearly 2
standard deviations above normal. ECMWF EFIs with respect to wind
gusts range from between 0.5 to 0.6 north of the I-90 corridor and
south of the MT Hwy 200 corridor, with the highest values located
along the Continental Divide (i.e. MacDonald Pass area). NBM4.3
probabilities for wind gusts in excess of 48kts across lower
elevations generally range from a 25-50% chance along and southwest
of a Cut Bank, to Great Falls, to Judith Gap line and along and
north of the I-90 corridor.

Accumulating Snow on Monday...

NBM4.3 probabilities for snowfall accumulations in excess of 4" from
late Sunday night through Monday night are in excess of a 70% chance
north of the Benchmark area along the Continental Divide, with even
a 30% chance in the Little Belts of Central Montana. Additionally
there is 60% or greater chance for snowfall accumulations of 6" or
more for the Marias Pass and Logan Pass areas over this same
timeframe, with ECMWF EFIs with respect to snow across the East
Glacier Park Region now in excess of 0.5. These increasing
probabilities and EFI values suggest the growing potential for some
winter weather related impacts to those traveling  on US Hwy 2 west
of Browning during the day on Monday. - Moldan

&&

.AVIATION...
21/12Z TAF Period

Fog and/or low stratus across portions of the Southwest and
Central Montana valleys will prevail through 15-18z Friday, with
LIFR/IFR/MVFR conditions at the KHLN and KBZN terminals over this
timeframe. Increased heating beyond 18z will lead to the dissipation
of the aforementioned fog/stratus, with VFR conditions expected
thereafter. Otherwise the only other concern throughout the
2112/2212 TAF period will be gusty surface winds, especially over
the plains of Central and North Central Montana. Additionally,
mountain wave turbulence and instances of low level wind shear
will be of concern through 18-24z Friday along the Rocky Mountain
Front. Mountain obscuration over Southwest and Central Montana
will decrease beyond 18z Friday. - Moldan

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  53  36  54  36 /   0   0   0   0
CTB  49  33  50  34 /   0   0   0   0
HLN  49  29  51  28 /   0   0   0   0
BZN  49  24  51  26 /   0   0   0   0
WYS  44  21  41  16 /   0   0   0   0
DLN  49  24  48  25 /   0   0   0   0
HVR  51  29  53  29 /   0   0   0   0
LWT  54  30  55  32 /   0   0   0   0

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Dense Fog Advisory until 10 AM MST this morning for Gallatin
Valley.

&&

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