930
FXUS65 KTFX 050416
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
916 PM MST Wed Dec 4 2024

.KEY MESSAGES...

 - Mild temperatures continue through Saturday, with a brief
   cooldown for the beginning of next week.

 - A few periods of gusty winds along the North Central Montana
   plains beginning late Thursday, with the strongest winds on
   Saturday.

 - Mountain snow with lower elevation rain transitioning to a
   wintry mix passes through Saturday evening through Monday
   morning.

&&

.UPDATE...

Main update for tonight into Thursday morning was to put out a
Dense Fog Advisory for plains areas along and northeast of a line
from Eastern Glacier County through the Snowy Mountains in
Southern Fergus County. Areas of fog and low clouds have already
reduced visibility to less than one mile across much of Toole,
Eastern Pondera, and Eastern Glacier Counties this evening, as
well as across eastern portions of Fergus and Blaine Counties.
Assuming the mid-level cloudiness clears out over the remainder of
the Advisory area in the next couple of hours, low clouds and fog
should spread into those areas as well. Although the reduced
visibility is the main concern, roads will likely become icy as
well, making travel additionally hazardous. Forecast models have a
frontal boundary along a Cut Bank to Great Falls line moving
slowly east more so onto the plains around and after midnight,
shifting winds more southwesterly and downsloping, which may help
erode the fog in the Cut Bank area into Eastern Pondera and Toole
Counties. The boundary is also causing some temperature
fluctuations here near the Great Falls International Airport this
evening, but its push east should help moderate temperatures
overnight here with a more sustained southwest wind. Have
therefore decreased the low for Great Falls a few degrees closer
to current temperatures, in anticipation of some warming
overnight. -Coulston

&&

.DISCUSSION...
/Issued 527 PM MST Wed Dec 4 2024/

 - Meteorological Overview:

An upper-level ridge remains in place through Saturday keeping
mostly dry weather for the area. A boundary along North Central
MT today will be capable in producing an isolated light snow
shower this afternoon. The persistent high pressure and calm
winds Thursday morning will also give the slight chance in
producing some low clouds/patchy fog along the Hi-Line. Thursday
and Friday, a pressure gradient sets up along the Northern Rocky
Mountain Front, which will produce gusty winds.

Heading into the weekend, the persistent upper-level ridge will
begin to break down. This break down of the ridge brings strong
mid level winds that will mix down to the surface. Strong winds
are anticipated along the Rocky Mountain Front and North Central
MT, especially the Montana Highway 200 corridor Saturday into
Sunday. Along with winds, a cold front will bring mountain
snow/rain transitioning to a wintry mix to lower elevations
Saturday evening through Monday morning.

Behind this system, ensemble models hint at another upper-level
ridge building in. This will keep most of the region dry, with
some lingering light snow in the mountains for the beginning of
next week.

 - Forecast Confidence & Scenarios:

There is good confidence for breezy to gusty winds increasing
along the Rocky Mountain Front and the Montana Highway 200
corridor Thursday and Friday. There has been a slight downtrend
for higher winds. Current probabilities give a 20% for 55 mph
around Cut Bank, and a 50-80% chance for other areas along the
Rocky Mountain Front. With the pressure gradient not looking as
strong as past wind events, no wind products are anticipated at
this time.

Confidence has been increasing for strong winds to move in
Saturday and Sunday for the Rocky Mountain Front and the Montana
Highway 200 corridor. There`s a 40-80% chance for 75 mph wind
gusts along the Rocky Mountain Front, and a 50-80% chance for
55 mph wind gusts in the Cut Bank area. Therefore, a High Wind
Watch was issued for those areas from early Saturday morning to
early Sunday morning. There is some spread in model guidance on
the higher end wind gusts values. There is medium confidence in
up to 80 mph wind gusts, with the strongest winds expected along
the cold frontal passage Saturday night. For the Montana Highway
200 corridor, there`s a 30-60% for 55 mph winds. The High Wind
Watch may be expanded later down the line if trends continue.

In terms of the winter weather Saturday through Monday morning,
the bulk of the snow looks to fall along the Little Belts region,
where there`s around a 40-50% chance for 6" of snow along King`s
Hill Pass. For other higher terrain areas across the region,
there`s a 20- 50% chance for 4" of snow. For lower elevations,
there is medium confidence for light snow mixing in Sunday
night/Monday morning. There is uncertainty in how much snow
accumulates, and it will largely depends on how quickly the cold
air moves in. Currently, there`s up to a 40% for 1" of snow.
-Wilson

&&

.AVIATION...
05/00Z TAF Period

VFR conditions are forecast to continue for much of North
Central, Central, and Southwest Montana through at least 06/00Z.

A high pressure ridge over the Western CONUS will continue the
northwesterly flow aloft over the area with passing high-level
cloudiness. However, areas of terrain-obscuring fog and low
clouds with MVFR/IFR conditions along and northeast of a KCTB to
KLWT line are likely to become more widespread through 06Z as
mid- level cloudiness decreases over that area. High-resolution
ensemble guidance gives a 40-70% probability for periods of
ceilings lower than 1000 feet and visibility less than 4SM. The
frontal boundary along this line is then forecast to shift east
across the area from 09Z through 18Z, allowing breezy southwest
winds to help erode any fog and low clouds.

Mid-level winds will not be exceptionally strong, so mountain
wave turbulence and low level wind shear should not be
significant. The strongest surface winds will remain along the
Rocky Mountain Front, where gusts in excess of 30 kt will be
common; however, these breezy winds should spread east to around
Interstate 15 by the end of the period, bringing westerly wind
gusts in excess of 25 kt at times to KCTB after 18Z. -Coulston

Refer to weather.gov/zlc for more detailed regional aviation
weather and hazard information.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  26  49  31  50 /   0   0   0   0
CTB  15  41  28  41 /   0   0   0   0
HLN  24  47  27  47 /   0   0   0   0
BZN  18  45  20  46 /   0   0   0   0
WYS   1  36   4  36 /   0   0   0   0
DLN  23  45  22  45 /   0   0   0   0
HVR  10  33  17  40 /  10   0   0   0
LWT  24  50  29  52 /   0   0   0   0

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Dense Fog Advisory until 11 AM MST Thursday for Bears Paw
Mountains and Southern Blaine-Eastern Glacier, Western Toole,
and Central Pondera-Eastern Pondera and Eastern Teton-Eastern
Toole and Liberty-Fergus County below 4500ft-Hill County-
Northern Blaine County-Western and Central Chouteau County.

High Wind Watch from late Friday night through late Saturday
night for East Glacier Park Region-Eastern Glacier, Western
Toole, and Central Pondera-Northern High Plains-Southern High
Plains-Southern Rocky Mountain Front.

&&

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