Lewistown, Montana 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

646
FXUS65 KTFX 200744
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
144 AM MDT Thu Aug 20 2026

.KEY MESSAGES...

 - It will be dry today.

 - Thunderstorms return Friday through this weekend with breezy
   conditions Saturday evening through Sunday.

 - It will warm up through Saturday and then cool back down to
   slightly below seasonal averages early next week.

&&

.DISCUSSION...

 - Meteorological Overview:

Today there is an upper-level ridge over North-central, Central, and
Southwestern Montana. This will keep warm and dry conditions for the
area on Thursday. Today and Thursday upper-level shortwaves will
move through the upper-level flow and keep temperatures slightly
cooler and bring breezy conditions to North-central, Central, and
Southwestern Montana. On Friday the upper-level ridge is over North-
central, Central, and Southwestern Montana. This will bring hot and
mostly dry weather to the area. An upper-level shortwave will move
through the upper-level flow and bring breezy conditions and an
increase in monsoonal moisture to North-central, Central, and
Southwestern Montana. Due to the increase in monsoonal moisture
Friday afternoon and evening there will be isolated showers and
thunderstorms in Southwestern Montana.

On Saturday an upper-level trough begins to move over North-central,
Central, and Southwestern Montana. Due to southwest flow aloft
monsoonal moisture remains over Montana on Saturday. 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 evening. On Sunday the upper-level trough is over North-
central, Central, and Southwestern Montana. This will cool down
temperatures slightly and due to the monsoonal moisture 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 there will be upper-level zonal flow over North-central,
Central, and Southwestern Montana. This will slightly cool down
temperatures and bring mostly dry weather to the area on Monday.
On Tuesday and Wednesday an upper-level ridge is over North-
central, Central, and Southwestern Montana. This will allow
temperatures to warm up on Tuesday and Wednesday. On Wednesday an
upper-level trough also begins to approach Montana. This will
bring a return of showers and thunderstorms to the area on
Wednesday. -IG

 - Forecast Confidence & Scenarios:

On Saturday there is a 25 - 35% chance for thunderstorms in
Southwestern Montana. On Saturday there is a 10 - 25% chance for
thunderstorms across North-central and Central Montana. On Sunday
there is a 30 - 40% chance for thunderstorms across Central and
Southwestern Montana. On Sunday there is a 15 - 30% chance for
thunderstorms across North-central Montana. Saturday through Sunday
there is a 30 - 50% chance for a quarter inch of rain or greater
across the mountains of Southwestern Montana. Precipitable Water
(PWAT) will increase this weekend which has the potential to lead
to localized flash flooding on burn scars with the stronger
thunderstorms.

On Saturday there is greater than a 50% chance for wind gusts of 25
mph or greater across North-central, Central, and Southwestern
Montana. On Saturday in northern Blaine County there is greater than
a 60% chance for wind gusts of 40 mph or greater. On Sunday there is
a 60 - 80% chance for wind gusts of 30 mph or greater across most of
North-central, Central, and Southwestern Montana. On Sunday there is
a 60% chance for wind gusts of 40 mph or greater along the Rocky
Mountain Front. On Sunday afternoon across North-central Montana
there is a 10 - 30% chance for wind speeds of 15 mph or greater
combined with relative humidity of 20% or less (red flag criteria).
On Sunday there is low confidence in relative humidity reaching
critical levels and so at this time it appears on Sunday there will
be at least elevated fire weather concerns due to gusty winds. -IG

&&

.AVIATION...
20/06Z TAF Period

VFR conditions will persist across the region with some surface
and slant range visibility reductions due to smoke at KEKS and
KGTF for tonight and the morning respectively. Mountains could
also be partially obscured from smoke plumes over Southwest MT.
Most terminals will see northwesterly winds pick up in the
afternoon after 21Z.


For KGTF: Winds will be light and variable overnight then start to
pick up out of the southwest by 17Z and shift to the northwest by
22Z. There could also be occasional gusts up to 15KT in the
afternoon impacting crosswind component thresholds. Visibility
could be slightly reduced from smoke for the afternoon until late
Thursday night with the potential for northerly outflows. - Akins

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  91  57  87  58 /   0   0   0   0
CTB  85  52  81  54 /   0   0   0   0
HLN  92  58  91  60 /   0   0   0  10
BZN  90  54  91  55 /   0   0   0  10
WYS  85  45  88  47 /   0   0   0  10
DLN  88  53  89  55 /   0   0   0  20
HVR  91  55  89  58 /   0   0   0   0
LWT  88  55  85  56 /   0   0   0   0

&&

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

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