National Weather Service Forecast for: Lewistown MT
Issued by: National Weather Service Great Falls, MT
Updated: 3:43 am MDT Jun 22, 2026
 
Overnight

Overnight: A 50 percent chance of showers and thunderstorms. Mostly cloudy, with a low around 45. Light and variable wind.
Chance
Showers
 Monday

Monday: Showers and thunderstorms likely, then showers and possibly a thunderstorm after noon. Patchy fog before 9am. High near 63. Light and variable wind becoming north northwest 5 to 9 mph in the morning. Chance of precipitation is 80%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.
Showers and
Patchy Fog
 Monday
Night
Monday Night: A 20 percent chance of showers and thunderstorms before 9pm. Partly cloudy, with a low around 38. Northwest wind 5 to 10 mph becoming west southwest after midnight.
Slight Chance
T-storms then
Mostly Clear
 Tuesday

Tuesday: Mostly sunny, with a high near 67. West wind 5 to 9 mph becoming north northwest in the afternoon. Winds could gust as high as 18 mph.
Mostly Sunny

 Tuesday
Night
Tuesday Night: Mostly cloudy, with a low around 43. North northwest wind 5 to 7 mph becoming light and variable in the evening.
Mostly Cloudy

 Wednesday

Wednesday: Partly sunny, with a high near 71. Calm wind becoming east around 5 mph in the afternoon.
Partly Sunny

 Wednesday
Night
Wednesday Night: Partly cloudy, with a low around 45. East southeast wind 6 to 10 mph, with gusts as high as 18 mph.
Partly Cloudy

 Thursday

Thursday: A chance of showers and thunderstorms after noon. Partly sunny, with a high near 75. Southeast wind around 6 mph.
Partly Sunny
then Chance
T-storms
 Thursday
Night
Thursday Night: A slight chance of showers and thunderstorms before midnight. Mostly cloudy, with a low around 47.
Slight Chance
T-storms then
Mostly Cloudy
Lo 45 °F Hi 63 °F Lo 38 °F Hi 67 °F Lo 43 °F Hi 71 °F Lo 45 °F Hi 75 °F Lo 47 °F

 

Overnight
 
 A 50 percent chance of showers and thunderstorms. Mostly cloudy, with a low around 45. Light and variable wind.
Monday
 
 Showers and thunderstorms likely, then showers and possibly a thunderstorm after noon. Patchy fog before 9am. High near 63. Light and variable wind becoming north northwest 5 to 9 mph in the morning. Chance of precipitation is 80%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.
Monday Night
 
 A 20 percent chance of showers and thunderstorms before 9pm. Partly cloudy, with a low around 38. Northwest wind 5 to 10 mph becoming west southwest after midnight.
Tuesday
 
 Mostly sunny, with a high near 67. West wind 5 to 9 mph becoming north northwest in the afternoon. Winds could gust as high as 18 mph.
Tuesday Night
 
 Mostly cloudy, with a low around 43. North northwest wind 5 to 7 mph becoming light and variable in the evening.
Wednesday
 
 Partly sunny, with a high near 71. Calm wind becoming east around 5 mph in the afternoon.
Wednesday Night
 
 Partly cloudy, with a low around 45. East southeast wind 6 to 10 mph, with gusts as high as 18 mph.
Thursday
 
 A chance of showers and thunderstorms after noon. Partly sunny, with a high near 75. Southeast wind around 6 mph.
Thursday Night
 
 A slight chance of showers and thunderstorms before midnight. Mostly cloudy, with a low around 47.
Friday
 
 A chance of showers and thunderstorms after noon. Partly sunny, with a high near 82.
Friday Night
 
 Showers likely and possibly a thunderstorm. Mostly cloudy, with a low around 48.
Saturday
 
 Showers likely and possibly a thunderstorm. Mostly cloudy, with a high near 68.
Saturday Night
 
 Showers likely and possibly a thunderstorm. Mostly cloudy, with a low around 42.
Sunday
 
 Showers likely and possibly a thunderstorm. Mostly cloudy, with a high near 60. Breezy.

 

Forecast from NOAA-NWS for Lewistown MT.