627
FXUS65 KTFX 181704
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1104 AM MDT Sat Oct 18 2025

Aviation Section Updated.

.KEY MESSAGES...

 - Strong to potentially high winds on Sunday, with the strongest
   winds occurring along and west of the I-15 corridor across
   Central and North Central Montana.

 - Precipitation chances increase tonight through Sunday along
   the Continental Divide, with increasing chances across
   Southwest Montana from Sunday afternoon through Sunday evening.

&&

.DISCUSSION...
/Issued 429 AM MDT Sat Oct 18 2025/

 - Meteorological Overview:

An active pattern is expected for much of the upcoming week, with
transitory ridging moving over the Northern Rockies today through
tonight ahead of a potent upper level shortwave and attendant
Pacific front which will then sweep east across North Central
through Southwest Montana from Sunday through Monday morning. High
temperatures today beneath the aforementioned ridge will
generally be near normal, with breezy but less windy conditions
compared to Friday and what is expected on Sunday. By this evening
a strengthening pressure gradient along the Rocky Mountain Front
and increasing ridgetop stability will lead to increasing winds
along and west of the I-15 corridor, especially near the immediate
eastern slopes of the Rocky Mountain Front. Precipitation chances
will also be on the increase through the overnight hours up and
down the Continental Divide from the Idaho to Canadian borders,
with precipitation chances peaking Sunday afternoon through
Sunday evening as the Pacific front and upper level trough axis
move overhead, mainly across the valleys of Southwest Montana and
in the mountains of Southwest through North Central Montana.
Southwest to west winds will also increase across the remainder of
North Central through Southwest Montana during the day on Sunday,
especially over the plains of Central and North Central Montana
and in the north- south orientated valleys of Southwest Montana.
Highs will warm thanks to these downsloping winds, with most
locations running above normal on Sunday.

Beyond Monday quasi-zonal flow with weak embedded ridges and
shortwaves will traverse east over the Northern Rockies, which will
help to maintain periods of mountain precipitation, breezy and
gusty surface winds, and above to well above normal temperatures.
- Moldan


 - Forecast Confidence & Scenarios:

High Winds on Sunday...

Climate anomaly indicators such as the NAEFS and ECMWF EFIs continue
to support a climatologically unusual wind event for portions of
the Northern Rockies, especially from the I-15 corridor across the
plains of Central and North Central Montana to the Continental
Divide. H700 flow within the NAEFS continues to be prog`d at
between 40-60kts over much of North Central through Southwest
Montana from 06z Sunday through 00z Monday, with deterministic
model guidance such as the GFS, NAM, and Canadian even suggesting
local maximums approaching 70kts over this same timeframe at
H700. Additionally the ECMWF EFIs for both sustained winds speeds
and gusts range from 0.6- 0.8 and 0.7-0.9 respectively along and
west of the I-15 corridor across Central and North Central
Montana, with values across the remainder of Central and North
Central Montana and south of the I-90 corridor in Southwest
Montana ranging from 0.5-0.7 and 0.6-0.8 respectively. Given that
the month of October sees a significant uptick in winds those EFI
values approaching 0.9 along and west of the I-15 corridor are
becoming more concerning for the potential of a very unusual to
extreme (high end) wind event. BUFKIT soundings for Cut Bank
points west to the Continental Divide continue to support an
atmospheric profile conducive for producing mountain wave
activity, especially during the morning hours on Sunday.
Additionally, BUFKIT soundings at Great Falls are even hinting at
the potential for mountain wave activity early Sunday morning, but
these signatures are not as strong as areas further north. NBM
4.3 probabilities continue to also trend up with the chance of
reaching or exceeding 55 mph at East Glacier, Browning and Cut
Bank, with these locations now ranging from 60%, 80%, and 85%
respectively; which is a 15-25% increase from 24hrs ago. The
probability for 65 mph at Browning and Cut Bank has also increased
15-20%, with probabilities now ranging from a 35% to 55% chance
respectively. Finally, the probability for wind gusts near 75 mph
has even jumped up to a 15% chance at Cut Bank, which seems valid
given the increasing EFI values mentioned earlier. Further south
across Cascade County the same trends upward with respect to wind
gusts have also been seen, with the chance of reaching or
exceeding 55 mph now ranging from 40-50% across much of the lower
elevations.

With probabilistic guidance still trending upwards with respect
to high wind criteria values I elected to add Cascade County below
5000ft to the on-going High Wind Watch. While confidence is very
high that portions of the High Wind Watch (i.e. Eastern Glacier,
Western Toole, and Central Pondera) will need to be upgraded with
future shifts I elected to not upgrade portions of the pre-
existing watch for the simple reason of upgrading/canceling all of
the watches at the same, along with giving one more model cycle
to fine tuning the timing of any potential upgrades.

Mountain Snow from Sunday morning through Monday morning...

ECMWF EFIs with respect to snow are beginning to suggest the
potential for some unusual snowfall amounts for portions of the
Continental Divide, generally across Northwest Beaverhead County and
then for areas north of the Montana Hwy 200 corridor. NBM
probabilities for 4" or more of snow throughout the timeframe
generally range from a 30-75% chance across the aforementioned
areas, with even a 5% and 40% chance for amounts to exceed 8" at
Marias and Logan Passes respectively. With the biggest push of
snow occurring during the daylight hours on Sunday most of the
snow that falls will be confined to non-asphalt surfaces, and for
that reason no winter highlights are planned at this time. With
that being said the strong west winds along the Rocky Mountain
Front combined with the falling snow will likely lead to
significant reductions in visibility, and travelers are urged to
exercise caution if driving on Sunday. - Moldan

&&

.AVIATION...
18/18Z TAF Period

Initial concern this TAF period will be for a period of breezy
surface winds this afternoon, mostly over the plains. Attention then
turns to late this evening into the overnight along the Rocky
Mountain Front, where the combination of increased cross barrier
flow and ridgetop stability will result in increasing mountain wave
turbulence. These stronger winds will begin to translate to the
surface over most other areas by late morning Sunday. Instances of
LLWS will be around late tonight into Sunday morning where flow
just off the surface increases, but does not mix down to the
surface.

Meanwhile, precipitation develops from north to south along the
Continental Divide tonight. It eventually makes its way eastward
across Southwest Montana through the day Sunday. Mountain snow and
lower elevation rain are forecast, with mountain obscuration
developing along with the precipitation. Areas on the plains largely
look to stay dry Sunday. -AM

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  56  46  60  40 /   0  30  30  30
CTB  53  40  56  37 /   0  30  30  30
HLN  55  41  55  39 /   0  10  80  50
BZN  52  37  54  32 /   0  10  90  50
WYS  45  25  47  21 /   0   0  90  70
DLN  53  35  55  30 /   0   0  80  20
HVR  55  37  61  36 /   0  30  50  20
LWT  51  36  58  37 /   0  20  50  30

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
High Wind Watch from late tonight through Sunday evening for
East Glacier Park Region-Northern High Plains-Southern High
Plains-Southern Rocky Mountain Front.

High Wind Watch from late tonight through Sunday evening for
Cascade County below 5000ft-Eastern Glacier, Western Toole, and
Central Pondera-Eastern Toole and Liberty.

&&

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