642
FXUS65 KTFX 181035
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
435 AM MDT Tue Aug 18 2026

Aviation Section Updated.

.KEY MESSAGES...

 - Showers and thunderstorms will affect the area this
   afternoon/evening.

 - Temperatures will be around seasonal averages throughout this
   week.

 - It will be dry Wednesday through Friday with thunderstorms
   returning this weekend with breezy conditions.

&&

.DISCUSSION...
/Issued 136 AM MDT Tue Aug 18 2026/

 - Meteorological Overview:

Today there will be zonal flow (west - east) over North-central,
Central, and Southwestern Montana. This will allow temperatures
to remain near seasonal averages with breezy conditions due to
modestly strong low and mid-level winds. There will also be
showers and thunderstorms across North-central, Central, and
Southwestern Montana this afternoon/evening. On Wednesday an
upper-level ridge begins to build back in across North-central,
Central, and Southwestern Montana. On Wednesday temperatures will
be around seasonal averages with dry weather. On Thursday the
upper-level ridge remains over North-central, Central, and
Southwestern Montana. This will keep warm and dry conditions for
the area on Thursday. On Wednesday and Thursday upper-level
shortwaves will move through the upper-level flow and bring breezy
conditions to North-central, Central, and Southwestern Montana.

On Friday the upper-level ridge remains over North-central,
Central, and Southwestern Montana. This will bring hot and dry
weather to the area. An upper-level shortwave will move through
the upper-level flow and bring breezy conditions to North-
central, Central, and Southwestern Montana. On Saturday an upper-
level trough begins to move over North-central, Central, and
Southwestern Montana. This will bring showers and thunderstorms
back to the area. Due to modestly strong low-level and mid-level
winds it will be breezy on Saturday. On Sunday the upper-level
trough is over North-central, Central, and Southwestern Montana.
This will cool down temperatures slightly and bring another round
of showers and thunderstorms to the area. On Sunday due to
modestly strong low and mid-level winds it will be breezy across
North-central, Central, and Southwestern Montana. On Monday an
upper-level ridge moves over North-central, Central, and
Southwestern Montana. This will bring warm and mostly dry weather
to the area on Monday. -IG

 - Forecast Confidence & Scenarios:

Today the Storm Prediction Center (SPC) issued a Marginal Risk (5%
chance for wind gusts of 58 mph or greater within 25 miles of a
point) for Choteau, Judith Basin, Fergus, and Southern Blaine
Counties. Today there is a 20 - 35% chance for thunderstorms
across North-central, Central, and Southwestern Montana.

Winds will increase and relative humidity will decrease Wednesday
through Sunday which will lead to elevated fire weather conditions.
Saturday evening through Sunday is the time period when the winds
increase the most and so Sunday afternoon currently has the greatest
risk for near critical fire weather conditions. This risk is
contingent on the track of the upper-level trough that moves through
Saturday evening into Sunday. -IG


&&

.AVIATION...
18/12Z TAF Period

VFR conditions will prevail at terminals during this TAF Period
outside of during any thunderstorms. After 18/18Z showers and
thunderstorms will be around all terminals. At this time there is
low confidence in thunderstorms affecting any of the terminals. All
thunderstorms will produce frequent lightning, a brief heavy
downpour, and gusty, erratic winds with the strongest
thunderstorms producing strong wind gusts. The greatest threat for
the strongest thunderstorms is at the KLWT terminal. During any
thunderstorms there will a brief visibility reduction down to
MVFR-levels and a brief period of mountain obscuration. During
this TAF Period smoke from wildfires will reduce slantwise
visibility at the KCTB and KHVR terminals. -IG

For KGTF: Winds will be light and variable until about 21Z when
they will increase to about 12 kt with gusts up to 16 kt and be
westerly. Between 21Z and 03Z there is a 50% chance for exceeding
a 15 kt crosswind. Winds will then become light and variable after
03Z. Between 21Z and 00Z there is a 15% chance for a
thunderstorm. The primary risks from any thunderstorms are gusty
winds exceeding the 15 kt crosswind threshold and frequent
lightning. -IG



&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  83  54  86  55 /  20  20   0   0
CTB  78  52  82  52 /  20  20   0   0
HLN  83  52  86  53 /  30  30   0   0
BZN  79  49  83  50 /  30  30   0   0
WYS  75  37  79  39 /  30  30   0   0
DLN  79  48  83  49 /  30  20   0   0
HVR  85  55  87  55 /  20  20   0   0
LWT  79  52  82  52 /  30  20   0   0

&&

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

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