635
FXUS65 KTFX 190518
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1118 PM MDT Tue Aug 18 2026

Aviation Section Updated.

.KEY MESSAGES...

- Scattered showers and thunderstorms this evening will diminish
  by Midnight.

- Dry and warm conditions settle in Wednesday and Thursday.

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

&&

.UPDATE...
/Issued 835 PM MDT Tue Aug 18 2026/
Current forecast is on track, with no update planned for this
evening. Showers/thunderstorms are diminishing from west to east
this evening, with most of the showers exiting the eastern
portions of the CWA by Midnight. Should be mostly dry across much
of the area the next few days, with warmer afternoon temperatures
ahead. Brusda

&&

.DISCUSSION...
/Issued 835 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...
19/06Z TAF Period

Conditions will be VFR overnight and tomorrow for most terminals
. There is a 10% chance for MVFR to IFR at KWYS for reduced
visibility from mist/fog from 19/09Z to 19/13Z however chances
could increase as observed RH is currently trending higher than
model guidance for the area.


For KGTF: VFR conditions will prevail through the period.
Prevailing winds will be at 8 to 12 KT and out of the West from
19Z to 22Z then shifting to the Northwest from 22Z to 20/03Z. Some
slight reductions to slant range visibility due to smoke may be
present until tomorrow evening. - 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