National Weather Service Forecast for: Lewistown MT
Issued by: National Weather Service Great Falls, MT
Updated: 12:31 am MDT Aug 20, 2026
 
Overnight

Overnight: Patchy smoke. Mostly clear, with a low around 54. Southeast wind around 6 mph.
Patchy Smoke

 Thursday

Thursday: Patchy smoke between 4pm and 5pm. Sunny, with a high near 89. Light and variable wind becoming northwest 5 to 9 mph in the morning. Winds could gust as high as 20 mph.
Patchy Smoke

 Thursday
Night
Thursday Night: Partly cloudy, with a low around 55. North northwest wind 5 to 9 mph becoming south southeast after midnight.
Partly Cloudy

 Friday

Friday: Mostly sunny, with a high near 86. Calm wind becoming east 5 to 8 mph in the afternoon. Winds could gust as high as 18 mph.
Mostly Sunny

 Friday
Night
Friday Night: Partly cloudy, with a low around 57. East wind around 11 mph, with gusts as high as 21 mph.
Partly Cloudy

 Saturday

Saturday: Partly sunny, with a high near 89. East southeast wind 6 to 8 mph.
Partly Sunny

 Saturday
Night
Saturday Night: A slight chance of showers and thunderstorms before 9pm, then a slight chance of showers between 9pm and midnight. Mostly cloudy, with a low around 57. South southeast wind 3 to 7 mph. Chance of precipitation is 20%.
Slight Chance
T-storms then
Mostly Cloudy
 Sunday

Sunday: A chance of showers and thunderstorms after noon. Mostly sunny, with a high near 88. Calm wind becoming west 5 to 8 mph in the afternoon. Winds could gust as high as 20 mph.
Mostly Sunny
then Chance
Showers
 Sunday
Night
Sunday Night: A slight chance of showers before midnight. Partly cloudy, with a low around 53.
Slight Chance
Showers then
Mostly Clear
Lo 54 °F Hi 89 °F Lo 55 °F Hi 86 °F Lo 57 °F Hi 89 °F Lo 57 °F Hi 88 °F Lo 53 °F

 

Overnight
 
 Patchy smoke. Mostly clear, with a low around 54. Southeast wind around 6 mph.
Thursday
 
 Patchy smoke between 4pm and 5pm. Sunny, with a high near 89. Light and variable wind becoming northwest 5 to 9 mph in the morning. Winds could gust as high as 20 mph.
Thursday Night
 
 Partly cloudy, with a low around 55. North northwest wind 5 to 9 mph becoming south southeast after midnight.
Friday
 
 Mostly sunny, with a high near 86. Calm wind becoming east 5 to 8 mph in the afternoon. Winds could gust as high as 18 mph.
Friday Night
 
 Partly cloudy, with a low around 57. East wind around 11 mph, with gusts as high as 21 mph.
Saturday
 
 Partly sunny, with a high near 89. East southeast wind 6 to 8 mph.
Saturday Night
 
 A slight chance of showers and thunderstorms before 9pm, then a slight chance of showers between 9pm and midnight. Mostly cloudy, with a low around 57. South southeast wind 3 to 7 mph. Chance of precipitation is 20%.
Sunday
 
 A chance of showers and thunderstorms after noon. Mostly sunny, with a high near 88. Calm wind becoming west 5 to 8 mph in the afternoon. Winds could gust as high as 20 mph.
Sunday Night
 
 A slight chance of showers before midnight. Partly cloudy, with a low around 53.
Monday
 
 Sunny, with a high near 81.
Monday Night
 
 Partly cloudy, with a low around 52.
Tuesday
 
 Mostly sunny, with a high near 83.
Tuesday Night
 
 A slight chance of showers. Partly cloudy, with a low around 53.
Wednesday
 
 A slight chance of showers. Mostly sunny, with a high near 85.

 

Forecast from NOAA-NWS for Lewistown MT.