395
FXUS65 KTFX 011820
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1120 AM MST Sun Nov 1 2026

.KEY MESSAGES...

 - Widespread precipitation today, with accumulating snow most
   prevalent over the higher terrain of southwest MT tonight into
   Monday morning.

 - Milder and drier conditions start by Tuesday and generally
   prevail through the rest of the upcoming workweek.

 - With lighter winds and areas of high humidity levels, pockets
   of fog will be possible during late overnight and morning
   hours, mainly impacting central and north-central MT and the
   southwest valleys during the upcoming work week.

&&

.DISCUSSION...

 - Meteorological Overview:

A moist southwesterly flow aloft continues to overrun a cooler
and nearly saturated air mass at the surface. 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. - RCG

As rain tapers off over Sunday night and Monday morning, lighter
winds and higher overnight humidity levels will allow for areas of
fog to potentially develop within central MT, north-central MT,
and the southwest valleys. Due to limited winds during the rest of
the Monday, there is the possibility that these areas of fog
remain socked in as they have the past few days, resulting in
daytime highs falling 5-10 degrees below what was expected in
those areas.

Looking towards the rest of the week, an upper-level ridge begins
to establish over the region beginning Monday evening. Accompanying
this ridge will be mild and dry weather. Although the upper-
level ridge is expected to weaken beginning Tuesday night, dry
and mild conditions are currently expected to remain in place
through at least Thursday afternoon. Although far out, a change in
the weather is anticipated on Friday due to an upper-level trough
beginning to move into the area, along with windier conditions.
-ESH


 - Forecast Confidence & Scenarios:

...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

...Fog during the upcoming week...

The main time period of concern will be Sunday night into Monday
morning as precip moves through the region and tapers off. Lighter
winds, along with residual moisture, will provide favorable
conditions for fog development. The main impact associated with
this would be a reduction in visibility and the potential for
freezing fog due to overnight lows expected to be near or below
freezing. If areas of denser fog develop, there is the potential
for that fog to remain socked in and keep daytime high
temperatures 5-10 degrees cooler than expected. Through the rest
of the upcoming work week, pockets of fog may develop overnight,
although these would likely be patchy and limited to areas near
bodies of water and valleys. -ESH


&&

.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  35  53  33  58 / 100   0   0   0
CTB  29  52  29  54 /  30   0   0   0
HLN  34  50  28  50 /  90  10   0   0
BZN  31  44  24  48 / 100  40   0   0
WYS  27  42  19  45 /  90   0   0   0
DLN  32  45  26  46 /  90  10   0   0
HVR  31  48  29  53 /  90   0   0   0
LWT  31  46  28  59 / 100  40   0   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