063
FXUS65 KTFX 011742
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1042 AM MST Sun Nov 1 2026

Aviation Section Updated.

.KEY MESSAGES...

- Periods of dense fog continue through the morning hours,
  most widespread over central and north-central Montana and the
  southwest valleys.

- Precipitation becomes more widespread today, with
  accumulating snow most prevalent over the higher terrain of
  southwest Montana tonight into Monday morning.

- Milder and drier conditions then generally prevail through much
  of the workweek.

&&

.DISCUSSION...

 - Meteorological Overview:

A moist southwesterly flow aloft continues to overrun a cooler
and nearly saturated air mass at the surface. This has maintained
an abundance of low clouds, while waves of light rain showers move
northward through the forecast area. Surface temperatures have
risen well above freezing for most locations, so freezing drizzle
or light freezing rain hasn`t been much of a problem tonight;
however, there is some stubborn colder air at the surface north of
the Hi-Line, mainly over northern Hill and Blaine counties, where
there maybe some isolated instances of freezing drizzle through
the morning hours. Also, some colder air is slowly seeping
southeastward over the plains along the Rocky Mountain Front.
Fortunately, these areas are mainly seeing fog rather than falling
precipitation. Speaking of fog, the aforementioned light
precipitation delayed the onset of fog development over much of
central and north-central MT tonight, but the fog looks to begin
expanding over the area heading towards the early dawn hours.
Also, dense fog has developed over the Gallatin Valley and looks
to expand to other southwest valleys as the night progresses.

The Pacific NW trough responsible for the moist southwesterly
flow ejects eastward towards the Northern Rockies and sends waves
of more widespread precipitation through the forecast area today
through Monday morning. This system will be undergoing weakening
and shearing as it approaches and its colder air aloft is not
scheduled to arrive until tonight into Monday morning. So snow
levels will be over 7000 ft for most locations, generally yielding
liquid precipitation at and below pass level. The one exception
to this will be along the Continental Divide where spotty light
snow will fall before tonight.

H700 temperatures finally fall to around -5C late night into
early Monday and this will bring more efficient accumulating snow,
heaviest over the Madison/Gallatin ranges above 6000 ft. There
will be a brief period with snow levels falling to the
valley/plains floors Monday morning, although it does not appear
that this will be long enough to support widespread accumulating
snow impacts. Northwesterly winds may also get gusty later
tonight, though gusts look to stay below 40 mph and the strongest
winds should quickly move east of the forecast area Monday
morning. Ensembles continue to favor ridging aloft to bring milder
and drier conditions for much of the upcoming workweek; however,
a weak system may move through around Wednesday and bring a few
isolated showers to the southwest and along the Continental
Divide. Forecast uncertainty increases towards the end of the
workweek, but most ensembles highlight zonal troughs bringing
breezy to windy conditions and mostly mountain precipitation
heading into next weekend. - RCG

 - Forecast Confidence & Scenarios:

...Areas of dense fog through the morning hours...

The fog has been most widespread over the plains west of I15 so
far tonight, but will begin to expand to other areas of central
and north-central MT with light shower activity diminishing and
ending. Also the southwestern valleys have also been observing
patchy dense fog development, which looks to expand in coverage
prior to the arrival of the more widespread precipitation later
this morning. Impacts will mostly be directly related from the
reduced visibility, but frost deposition or even some freezing
drizzle may cause some slippery spots to develop on roadways,
especially the bridges and elevated surfaces. These roadway
impacts will generally be confined to plains locations along and
west of I15. The dense fog advisory covering much of
central/north-central MT was left as is and some southwest valleys
were added to the advisory, including the Bozeman, Dillon, and
Helena areas.

...Light mountain snow and lower elevation rain and snow Sunday
through Monday morning...

The main trough swings through today through early Monday and
brings a wave of widespread precipitation to much of the forecast
area. Aside from some light snow along the Continental Divide and
perhaps some spotty freezing drizzle over the plains west of I15,
most of the precipitation will be falling in the form of rain
until the colder air aloft moves in tonight. The overall pattern
and NBM probabilities continue to favor elevations over 6000 ft in
the Madison and Gallatin ranges for the best chance (60 to 80%)
of snowfall amounts in excess of 3 inches. Lighter snows,
generally up to a couple inches, look to fall along the
Continental Divide and the central island ranges. The colder air
is still not looking to be optimally aligned with the moisture for
lower elevation snows, even in the Gallatin Valley where
probabilities for 2 inches of snow fell from around 30% to around
10%. Decided to hold off on issuing any winter advisories with
this forecast package given the brief window of opportunity for
accumulating snow at and below pass level and H700 temperatures
trending upward ever so slightly. - RCG

&&

.AVIATION...
01/18Z TAF Period

Dense fog is starting to lift over North Central MT as of 18z
today, as light rain moves northward into North Central MT. Low
clouds/ceilings will affect all sites through the period. There is
the potential that some dense fog could redevelop once again
tonight. Mountains/passes will be obscured across the CWA by
precip/low clouds. Brusda

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  44  34  52  33 /  90  90  10   0
CTB  43  28  51  29 /  80  40   0   0
HLN  44  33  49  28 / 100  90  10   0
BZN  43  31  44  24 /  90 100  50   0
WYS  41  26  42  19 / 100 100  10   0
DLN  41  32  44  26 / 100  90  10   0
HVR  45  31  47  29 /  80 100  10   0
LWT  48  30  45  28 /  80 100  70   0

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Dense Fog Advisory until noon MST today for Bears Paw Mountains
and Southern Blaine-Beaverhead and Western Madison below 6000ft-
Canyon Ferry Area-Cascade County below 5000ft-Eastern Glacier,
Western Toole, and Central Pondera-Eastern Pondera and Eastern
Teton-Eastern Toole and Liberty-Fergus County below 4500ft-
Gallatin Valley-Helena Valley-Hill County-Judith Basin County
and Judith Gap-Madison River Valley-Missouri Headwaters-Northern
Blaine County-Northern High Plains-Southern High Plains-Western
and Central Chouteau County.

&&

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