516
FXUS65 KTFX 171158
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
458 AM MST Mon Nov 17 2025

Aviation Section Updated.

.KEY MESSAGES...

- There will be periods of overnight and morning patchy
  fog development for the next day or so, mostly over and near
  river valleys.

- Passing weather systems will bring spotty areas of light rain
  and mostly mountain snow through Wednesday.

- A more progressive weather pattern brings a return of breezy to
  windy conditions and mountain snow this weekend, followed by a
  shift to more wintry conditions heading into the Thanksgiving
  holiday.

&&

.DISCUSSION...
/Issued 244 AM MST Mon Nov 17 2025/

 - Meteorological Overview:

A moist, but weak, southwesterly flow aloft will persist until
Wednesday when a Pacific trough passes through the Northern
Rockies. This will maintain variably cloudy skies and periods of
lighter end rain and snow. Snow levels will be lowest on Wednesday
while the trough axis moves overhead; however, negligible
precipitation amounts and the lack of colder air aloft will offer
little support for accumulating snow. Lingering moisture and light
winds throughout the atmospheric profile will also encourage
areas low stratus and patchy fog to develop over the next couple
of days. This looks to be most prevalent during the overnight and
morning hours near river valleys.

Drier conditions move in for the second half of the workweek with
another Pacific trough diving southeastward into Great Basin and
southwest US. Then the upper level jet moves into the Northern
Rockies this weekend and brings periods mostly mountain snow,
breezy to windy conditions, and cooler temperatures. A series of
troughs may then bring colder temperatures and even periods of
snow for the week of Thanksgiving, though model guidance has been
divergent, especially in terms of trough amplitude and timing.
- RCG

 - Forecast Confidence & Scenarios:

Scattered areas of light rain and snow through Wednesday...

Rain and snow associated with an approaching Pacific weather
system looks to be light and scattered in nature. Temperatures
aloft will not be favorable for accumulating snow until the trough
axis moves overhead on Wednesday. Even then, probabilities for
one inch of snow or more will be around 20% in the mountains and
near zero for lower elevations.

Increasing winds and mountain snow this weekend...

Winds increase heading into the weekend while mountain snow
returns, mostly along the Continental Divide. Recent ensemble runs
have begun to favor the jet stream setting up a little farther
north with shallower troughing. If this trend continues, it would
shift the mountain snow farther north, just clipping the Rocky
Mountain Front. Areas of higher terrain to the south and the
plains/valleys would see little to no precipitation. A more
southerly trajectory would bring more mountain snow, especially
the northwesterly upslope areas, including the central island
ranges and the Madison and Gallatin ranges. The strongest
shortwave and best chance for precipitation looks arrive Saturday
night into Sunday. Westerly surface winds will also be on the
increase with many central and north-central locations seeing
winds in the 30 to 50 mph range.

More wintry pattern shift for the week of Thanksgiving...

Nearly all ensemble members usher in below average temperatures
for the days leading up to Thanksgiving, but only around a third
of them highlight impactful accumulating snow. There are still
significant differences with trough amplitude and timing and there
also has been poor model run to run consistency. Overall,
preparations should be made for the arrival of the coldest
temperatures of the season so far with probabilities for below
freezing highs climbing above 70% for most areas next Tuesday
through Thursday. - RCG

&&

.AVIATION...
17/12Z TAF Period

Weak southwesterly flow aloft will maintain variable cloudiness and
spotty areas of light rain for much of the TAF period. Overnight fog
development in the KHVR area has been precluded by high clouds, but
there is still a window for IFR/LIFR impacts through 17/18Z. Low
stratus and fog development looks to impact KCTB and KHVR again
after 18/06Z. General VFR conditions will prevail for the other
terminals, but there will be some mountain obscuration, mostly along
the Continental Divide and over southwest MT. - RCG

The KWYS TAF will not be issued until airport operations resume
next spring.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  60  36  54  33 /  10  10   0  20
CTB  57  30  50  28 /  10  10  10  10
HLN  55  34  53  32 /  10  10  10  20
BZN  54  33  53  30 /  10  10  10  20
WYS  41  28  43  23 /  50  40  20  20
DLN  52  32  51  28 /  10  10   0  10
HVR  50  30  47  28 /   0  10  10  20
LWT  57  34  53  30 /   0  10  10  20

&&

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

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