821
FXUS65 KTFX 181716
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1016 AM MST Tue Nov 18 2025

Aviation Section Updated.

.KEY MESSAGES...

 - Variably cloudy skies with spotty areas of light rain and
   mostly mountain snow continue through Wednesday.

 - Fast moving weather systems bring breezy to windy conditions
   and periods of mountain snow this weekend.

 - A shift to colder temperatures and periods of snow expected
   heading into Thanksgiving.

&&

.UPDATE...
/Issued 825 AM MST Tue Nov 18 2025/

Fog along the Hi-Line is expected to lift by the late morning.
Visibilities as of 8:20 AM are around 1SM to 3SM from Browning to
Shelby and around 3SM east of Havre. The main concern will be
along US-2 where sudden changes/reductions in visibility are
possible. But as of yet dense fog has not materialized yet so
there is no need for an advisory.

Otherwise no major changes were made to the going forecast. -thor


&&

.DISCUSSION...
/Issued 825 AM MST Tue Nov 18 2025/

 - Meteorological Overview:

A moist, but weak, southwesterly flow aloft persists until
Wednesday when a Pacific trough passes through the Northern
Rockies. This will maintain variably cloudy skies and spotty areas
of light precipitation. 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. Overnight and morning low
stratus and patchy fog will continue to be a concern through
Wednesday morning, especially near the Hi-Line; however, abundant
mid- and high level clouds should limit the overall coverage and
impact from dense fog.

Weak ridging aloft will bring dry and mild conditions for the
second half of the work week while the northern jet stream stays
in Canada and a closed low slides down the California coast. The
upper level jet moves southward into the Northern Rockies this
weekend and brings periods breezy to windy conditions, cooler
temperatures, and some mountain snow. A northwesterly flow aloft
develops and sends a series of colder troughs through the state
heading into the Thanksgiving holiday. This looks to bring periods
of mostly light snow and the coldest temperatures of the season so
far. -RCG

 - Forecast Confidence & Scenarios:

Scattered areas of light rain and snow through Wednesday

A tightly wound mid-level low will bring the heaviest
precipitation along the Northern Rocky Mountain Front today,
roughly between 8 am and 2 pm. While there will be a narrow stripe
of -10c temperatures at 700 mb, it is not ideally aligned with
the area of heaviest precipitation. This should confine the more
impactful accumulating snow above Marias Pass where there is less
than a 20% chance for an inch of snow. Colder west to
northwesterly flow moves in on Wednesday when snow levels may
briefly fall to the valleys and plains. Accumulations, if any,
look to be minimal with probabilities for one inch of snow or more
around 20% over the higher terrain near Glacier National Park and
near zero for other areas.

Increasing winds and mountain snow this weekend

A tightening surface pressure gradient will bring an initial wave
of windy conditions to the Rocky Mountain Front on Friday.
Probabilities for 55 mph+ gusts increase to around 80% over the
eastern foothills of the Rocky Mountain Front eastward to the
Browning area. Similar probabilities remain in place on Saturday,
but drop off on Sunday despite some deterministic guidance
highlighting more windy conditions. Winds will also be on the
increase in other areas with many central and north-central
locations seeing gusts in the 30 to 50 mph range. The trend for
much shallower shortwaves passing through this elevated west to
northwest flow aloft continues, which equates to less
precipitation for the weekend. The higher terrain of the Rocky
Mountain Front looks to be the recipient of accumulating snow with
around a 50% chance for a 1 to 3 inch of snow at Marias Pass
Saturday night into Sunday.

Colder pattern shift for the week of Thanksgiving

Ensembles are highlighting a strong trough and attendant cold
front to surge through the Northern Rockies sometime Monday or
Tuesday. The dynamics look supportive for a period of strong,
gusty winds and locally intense snow showers. This will usher in a
more active and colder pattern, but there are still differences
with trough amplitude and timing and the poor model run to run
consistency has continued. Overall, there`s an expectation for
the coldest temperatures of the season thus far with probabilities
for below freezing highs climbing above 70% for most areas by
Thanksgiving. - RCG

&&

.AVIATION...

18/18Z TAF Period

The initial concern this TAF period will be for some lingering low
clouds/fog over the plains through early afternoon. Otherwise the
concern today will be for isolated pockets of precipitation,
mainly over the mountains.

Heading into late tonight, a cold front drops south from Canada,
resulting in a wind shift to a more northerly direction with at
least brief instances of low clouds at most terminals Wednesday
morning. A few instances of rain or snow showers will move in ahead
of and with the front Wednesday morning, but was too low confidence
to warrant mention in any TAFs at this time. Mountains looked to
be obscured at times near and behind the front. -AM

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  57  29  44  25 /   0  10  10   0
CTB  52  29  44  20 /  10  10  10   0
HLN  55  30  45  26 /  10  10  20   0
BZN  54  30  46  25 /   0  10  20   0
WYS  43  26  43  22 /  20  10  40  10
DLN  52  29  47  25 /   0   0  10   0
HVR  49  27  43  19 /  10  20  10   0
LWT  56  27  42  23 /   0  10  10   0

&&

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

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