214
FXUS65 KTFX 182346
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
546 PM MDT Tue Aug 18 2026

Aviation Section Updated.

.KEY MESSAGES...

- Scattered showers and thunderstorms develop this afternoon and
  evening, with isolated severe winds and hail possible.

- Dry and warm conditions settle in Wednesday and Thursday.

- Breezy winds and showers and thunderstorms move in through the
  weekend.

&&

.DISCUSSION...
/Issued 1247 PM MDT Tue Aug 18 2026/

 - Meteorological Overview:

For the rest of today, a small shortwave trough moving through the
region will continue to develop scattered showers and thunderstorms
across the region. Weak instability of 500-1,000 j/kg and mid level
moisture will help aid in thunderstorm development. One thing that
is lacking is shear, with ~20kts of shear (closer to 30kts in
Southwest MT) will limit longevity of storms. However, deep
mixing and a dry surface layer creates a conducive environment
for gusty to isolated severe wind gusts for mature/collapsing
storms. DCAPE reaching near 1,000 j/kg supports this environment.
Decent mid level lapse rates also supports a localized hail
threat with the strongest storms.

After this shortwave trough passes, upper-level ridging builds in
for Wednesday and Thursday. The lack of forcing will keep the
region dry. Upper-level ridging continues into Friday with a
trough building in along the West Coast U.S. Though, embedded
vorticity maximums and an increase in monsoonal moisture returns
showers and thunderstorm chances.

The trough propagates east over the weekend and into early next
week, keeping showers and thunderstorms in the forecast. With the
upper-level ridge breakdown comes an increase in mid level winds
Saturday into Sunday and therefore surface winds. There remains some
uncertainty in how strong the winds gets but there is good
confidence for breezy winds for the weekend.

 - Forecast Confidence & Scenarios:

There is some uncertainty in how strong the winds get this
weekend. However there is better agreement in the timing of the
winds (late Saturday through Sunday morning. Right now, there`s a
good coverage of 30-70% chances for 30 mph gusts Saturday and
Sunday, with 20-40% chances for 40 mph winds along the Hi-line
Sunday. Seems like the main limiting factor for fire weather is
low confidence for critical relative humidities, but can`t rule
out elevated fire weather concerns if winds keep trending this
weekend. Another thing to watch for this weekend is high PWAT
values of an inch bringing a localized flash flooding threat to
burn scars. -Wilson

&&

.AVIATION...
19/00Z TAF Period

Scattered showers and thunderstorms are moving through Central MT
and will end by 19/04Z. Primary threats remaining with the stroms
are brief strong gusts from outflows up to 45 KT, cloud-to-ground
lightning, and localized heavy rain. Conditions will be VFR this
evening into tomorrow morning for most terminals however there is
a 40% chance for MVFR and 10% for IFR conditions at KWYS for
fog/mist and ceilings from 19/09Z to 19/12Z.

For KGTF: VFR conditions will prevail with the passing of the
thunderstorms. Winds will predominantly be out of the Southwest
through the period from 8 to 12 KT on average however there is a
small chance for brief variable wind shifts until 19/02Z due to
residual outflow boundary interactions. - Akins


&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  54  86  55  85 /  20   0   0   0
CTB  52  82  52  78 /  20   0   0   0
HLN  52  86  53  89 /  30   0   0   0
BZN  49  83  50  90 /  30   0   0   0
WYS  37  79  39  84 /  30   0   0   0
DLN  48  83  49  86 /  20   0   0   0
HVR  55  87  55  87 /  20   0   0   0
LWT  52  82  52  85 /  20   0   0   0

&&

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

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