101
FXUS65 KTFX 210759
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
159 AM MDT Fri Aug 21 2026

.KEY MESSAGES...

- Very warm and dry conditions prevail again today with widely
  scattered gusty showers and thunderstorms moving in from the
  southwest this evening into tonight.

- After another very warm day on Saturday, scattered afternoon and
  evening showers and thunderstorms will develop in a southwest to
  northeast fashion, some storms will contain strong, gusty
  winds, heavy downpours capable of localized flooding over burn
  scars, and dangerous cloud to ground lightning.

- A surface front will bring gusty winds and elevated fire weather
  concerns on Sunday, there will also be a few lingering showers
  and storms east of I15.

- There will be a modest cooldown early next week with some
  widely scattered showers and storms, mostly over southwest
  Montana.

&&

.DISCUSSION...

 - Meteorological Overview:

Strong ridging aloft will remain in place today before a trough
moving onto the Pacific NW coast brings a more unstable
southwesterly flow to the Northern Rockies tonight into Saturday.
Very warm and dry conditions generally prevail through the weekend
even while the ridge breakdown process takes place. Most lower
elevation locations will see afternoon highs well into the 80s to
the lower 90s. Subtle shortwaves will begin moving through and
interacting with increasing instability this evening into tonight.
This will send a wave of widely scattered high based showers and
thunderstorms moving in a southwest to northeast fashion this
evening into tonight with the primary impact being localized gusty
winds and lightning, especially for central and southwest MT.

Stronger shortwaves look to send a more impactful wave showers
and thunderstorms through the forecast area late Saturday
afternoon into Saturday night. ML CAPE doesn`t look exceptionally
high in the 400 to 900 J/kg range, but forcing from the shortwave
will make up some of the void and very warm and dry sub cloud
layers will increase instances of strong gusty winds up to and
exceeding 60 mph, especially if linear upscale growth takes place.
Hail and brief downpours downpours capable of flash flooding of
normally flood prone areas will also be present with bulk shear
generally above 25 kts and PWATS approaching and even surpassing
the one inch mark in some cases. The focus of this activity will
be over southwest MT and and along the Continental Divide, though
at least some of it will move northeastward onto the plains during
the overnight hours.

The Pacific NW trough will swing northeastward through W MT and
into Canada on Sunday while its attendant surface front traverses
the CWA and brings gusty westerly winds and elevated fire weather
conditions. There will also be lingering instability for widely
scattered showers and thunderstorms, some on the strong side,
mainly for locations east of I15. Temperatures modestly cooldown
Monday and Tuesday with some shower and thunderstorm activity in
southwest MT. This looks to be followed by ridging aloft briefly
rebuilding before another Pacific trough approaches during the mid
to latter part of next week. - RCG

 - Forecast Confidence & Scenarios:

Scattered shower and thunderstorm activity this evening through
Sunday, strongest and most widespread Saturday...

An unstable southwesterly flow aloft will send multiple waves of
showers and thunderstorms through the forecast areas this evening
through Sunday. The initial wave will move into southwest MT by
this evening before moving northeastward during the overnight
hours. This activity will be isolated in nature and mostly high
based with little precipitation. The primary concern will be
localized gusty winds over 30 mph and lightning, mostly for
southwestern locations.

The stronger shortwave energy arrives Saturday afternoon into
Saturday night. Strong gusty winds in excess of 60 mph and
lightning will be the primary hazards on Saturday, especially if
the storms become linear and undergo upscale growth. This threat
will be highest over southwest MT and along the Continental
Divide. Some weakening is expected with this activity as it moves
northeastward, though these same hazards apply to plains locations
as well. In addition to the winds, there will be localized heavy
downpours capable of flash flooding of burn scars and other flood
prone locations, mainly in southwest MT where there is around a
10% chance for excessive rainfall and localized flooding. The
focus of this activity shifts eastward on Sunday with a few
stronger storms for locations east of I15. Central/north-central
locations east and southeast of the highway 87 corridor will see
the strongest storm ceiling with strong, gusty winds, hail, and
downpours all on the table. - RCG

&&

.AVIATION...
21/06Z TAF Period

VFR conditions will prevail across the region through the period
however there is a 30% chance of slight visibility reduction due
to mist for the KCTB area. An outflow boundary is currently
moving southward across KCTB, KHVR, and KGTF briefly increasing
winds up to 15 - 25 KT until 07Z. Some smoke will also obscure
distant mountain ranges across the region through the period.
Scattered dry thunderstorms over Southwest MT are expected to
develop after 22/05Z Friday night primarily impacting KEKS and
KBZN during the period. Primary threats for these storms will be
strong gusts and cloud-to-ground lightning.

For KGTF: VFR conditions for the period. Winds will be mostly
light and variable tonight with a brief possible northerly gust of
up to 18 KT between 06Z and 07Z. Then winds will shift
northeasterly tomorrow afternoon. Currently, next chance for
thunderstorms is predicted to be Saturday morning after 22/16Z. -
Akins

&&

.FIRE WEATHER...

The fire weather concerns begin when isolated showers and storms
with cloud to ground lightning and little precipitation pass
through this evening into tonight. Even though this activity will
be isolated, some new fire starts can`t be ruled out. More
productive storms move in on Saturday, but again the presence of
cloud to ground lightning may ignite new fire starts. The most
cornering day will be on Sunday when a surface front brings gusty
westerly winds amid continued very warm and dry conditions. The
timing of this front will ultimately determine how long the dry
windy conditions persist. The latest NBM probabilistic guidance
highlights large areas of north-central and portions of southwest
Montana with over a 60% chance for wind gusts over 30 mph.
Although the fuels aren`t quite as dry as they were in earlier in
the month, elevated fire conditions will be present and the wind
may be enough to ignite any lightning caused hold over fires from
Friday and Saturday`s storms. - RCG

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  87  59  91  60 /   0  20  20  30
CTB  82  54  84  56 /   0  10  20  10
HLN  92  60  90  58 /   0  30  30  50
BZN  91  57  88  53 /  10  20  40  60
WYS  89  50  83  45 /  10  20  40  50
DLN  90  57  86  51 /  10  30  50  70
HVR  89  59  93  60 /   0  10  20  10
LWT  85  57  88  58 /   0  10  20  30

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
None.
&&

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