041
FXUS65 KTFX 160604
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1204 AM MDT Sun Mar 16 2025

Aviation Section Updated.

.KEY MESSAGES...

 - Periods of mostly mountain snow continue through Tuesday, with
   the most widespread snowfall expected Sunday and Monday.

 - Windy conditions are expected Sunday and Sunday night along
   the Rocky Mountain Front and over portions Southwest Montana,
   particularly for the narrow south to north oriented southwest
   valleys and mountain tops.

 - A brief period of drier conditions is expected for the mid-
   week period before another round of Pacific weather systems
   brings more unsettled conditions heading towards next weekend.


&&

.UPDATE...
/Issued 827 PM MDT Sat Mar 15 2025/
Updated forecast is out. The main adjustment this evening was to
the high wind watch. The high wind watch ended for the Canyon
Ferry zone, but was changed to a high wind warning for the
Bozeman, Whitehall and Boulder areas. Overall, there looks to be
enough mixing when the front moves through to produce wind gusts
near/above warning criteria for the zones changed to a high wind
warning. The remainder of the high wind warning also looks on
track. Overall, Sunday afternoon/evening looks to be the period of
strongest winds.

Further north, light snow continues to affect the Northern Rockies
this evening, with accumulating snow falling as far east as East
Glacier Park. Thus the winter weather advisory will continue for
this area overnight. The rest of the forecast is on track. Brusda

&&

.DISCUSSION...
/Issued 144 PM MDT Sat Mar 15 2025/

 - Meteorological Overview:

A series of Pacific weather systems will move through the
Northern Rockies through Tuesday, bringing periods of mostly
mountain snow, scattered lower elevation rain/snow showers, and
breezy to windy conditions. Snow for today will be most impactful
along the Northern Rocky Mountain Front. There will be some
accumulating snow in the southwest mountains as well, but amounts
greater than 2 inches will mostly be limited to the higher peaks.
Lower elevation scattered rain and snow showers will be most
prevalent over Southwest Montana. A weak frontal boundary over
the plains will retreat to north, with near average highs
expected this afternoon, except a little cooler along the Hi-
Line.

An elevated warm front will bring another round of mostly
mountain snow tonight into Sunday morning, with the locations
along the Continental Divide and the higher terrain of the
southwest seeing most of the snow on Sunday. West to
southwesterly flow aloft increases markedly ahead of the Pacific
cold front and brings breezy to windy conditions for most
locations Sunday into Sunday night. The most anomalously strong
winds, according to climate anomaly analysis data and NBM
probabilistic guidance, will be over the southwest where H700
winds peak in the 45 to 60 kt range by Sunday evening, which is
about 3 to 4 standard deviations above climatology.

The trough axis will approach the Northern Rockies Sunday night
when the most widespread snow is expected. The snow then begins
to diminish in a northwest to southeast fashion during the day on
Monday, essentially retreating to Southwest Montana by Monday
afternoon and evening. Cold northwesterly flow behind the trough
will bring another round of lighter end snows before ridging
aloft briefly dries things out on Wednesday.

The parade of Pacific storms return heading into next weekend for
more periods of mostly mountain snow, breezy to windy conditions,
and near average temperatures. - RCG


 - Forecast Confidence & Scenarios:

Snow along the Northern Rocky Mountain Front through Sunday
morning...

The snow will be most impactful at Marias Pass and the higher
terrain around Glacier National Park. Snowfall exceedence
probabilities support an additional 2 to 6 inches of snowfall on
the Pass. Current camera images from Essex (just west of Marias
Pass) show that roads remain mostly wet, though MDT reports that
roads may be snow covered around Marias Pass. Nevertheless, the
Winter Weather Advisory will remain in effect, and be alert for a
quick freeze up on the roads after sunset.

Snow Sunday through Tuesday...

The elevated warm front does bring additional snow tonight into
Sunday, again most notably to the Marias Pass Glacier National
Park area. The winter weather advisory mentioned above will cover
the snow through noon on Sunday. Then milder temperatures, both
at the surface and aloft, should limit impacts through Sunday
afternoon. The other main areas with potential winter weather
impacts will be over the Chief Joseph Pass area and the
Centennial Mountains where probabilities for 2 inches of snow or
more are running in the 80 to 90% range on Sunday. These areas
will be evaluated for winter weather advisories, particularly if
the most of the snow looks to occur during the morning hours.

The most widespread snow arrives Sunday night through Monday, but
snowfall probabilities are still not overly concerning for most
locations. If there`s any area to really monitor, it`s the
Madison and Gallatin mountains on Monday when deterministic
forecasts have snowfall amounts in excess of 6 inches over areas
of higher terrain. Also, heavier convective snow banding can
easily produce localized higher amounts. There will be more
mountain snow and potential convective enhancement on Tuesday,
but this activity looks to be lighter and more disorganized.

Sunday`s strong wind potential along the Rocky Mountain Front,
plains, and Southwest Montana...

Some deterministic guidances highlight H700 southwesterly flow
increasing up to around 70 kts over Southwest Montana late Sunday
afternoon and evening. This definitely has the potential to
transfer to the surface, particularly for the mountain tops and
the south to north oriented valleys like the Madison and
Beaverhead Valleys. However, this does not come without some
uncertainties of course. Firstly, the flow aloft increases
throughout the day, but doesn`t peak until the end of the day.
Then, the surface pressure gradient isn`t as robust as I would
like to see it, especially for locations north of I90. I did
upgrade the high wind watch to a warning for the areas with the
highest probabilities, which include the Madison and Beaverhead
valleys, the Beaverhead Mountains, the Bridger Mountains, and the
Madison/Gallatin Ranges. All other areas to the north and west
were left as a watch for now, though the Watch for the Big Hole
Valley has been cancelled as of this afternoon. I also considered
delaying the timing until sometime in the afternoon with the
strongest winds expected in the evening, but declined to do so
given some stronger gusts may develop prior to the afternoon,
especially in the Madison Valley and the over the higher mountain
peaks.

Westerly flow aloft isn`t as robust along the Rocky Mountain
Front and the plains, but diurnal mixing and or scattered
convective showers may serve to mix 40 to 50 kt H700 wind to the
surface. Given the lack of a surface pressure gradient and low
wind gust exceedence probabilities (40 to 60%), I held off on
wind products for now. - RCG/Ludwig

&&

.AVIATION...
16/06Z TAF Period

Strong west to southwesterly flow aloft and an approaching
Pacific trough will bring increased surface winds, mountain wave
turbulence, and instances of low level wind shear for much of the
TAF period. The worst conditions are expected over Southwest
Montana between 16/20 and 17/06Z when mountain top winds peak in
the 50 to 60 kt range. VFR conditions are generally expected;
however, there will be considerable mid- and higher level
cloudiness and periods of mostly mountain precipitation will
maintain terrain obscuration for much of the period. While most
of the precipitation will be confined to the mountains, scattered
lower elevation showers may bring periods of MVFR conditions,
particularly for KBZN, KEKS, and KHLN in the afternoon and evening
hours. - RCG

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

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  30  53  34  47 /  10  20  60  20
CTB  25  46  28  43 /  10  30  30  20
HLN  28  51  31  45 /  20  50  80  30
BZN  21  47  29  40 /  50  40  70  60
WYS  15  38  27  38 /  70  90  80  90
DLN  25  47  32  43 /  10  40  70  60
HVR  24  49  27  47 /  30  20  40  20
LWT  26  47  30  42 /  30  20  60  20

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until noon MDT Sunday for East Glacier
Park Region.

High Wind Warning from noon Sunday to midnight MDT Sunday night
for Elkhorn and Boulder Mountains-Gallatin Valley-Missouri
Headwaters.

High Wind Warning from 6 AM Sunday to midnight MDT Sunday night
for Beaverhead and Western Madison below 6000ft-Big Belt,
Bridger and Castle Mountains-Gallatin and Madison County
Mountains and Centennial Mountains-Madison River Valley-Ruby
Mountains and Southern Beaverhead Mountains.

&&

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