National Weather Service Forecast for: Lewistown MT
Issued by: National Weather Service Great Falls, MT
Updated: 7:41 pm MDT Jun 18, 2026
 
Tonight

Tonight: Partly cloudy, with a low around 39. Northwest wind around 6 mph becoming calm in the evening.
Partly Cloudy

 Juneteenth

Juneteenth: Mostly sunny, with a high near 70. Calm wind becoming east 5 to 8 mph in the afternoon.
Mostly Sunny

 Friday
Night
Friday Night: Mostly cloudy, with a low around 45. East southeast wind 8 to 15 mph, with gusts as high as 26 mph.
Mostly Cloudy

 Saturday

Saturday: A slight chance of showers between noon and 3pm, then a slight chance of showers and thunderstorms after 3pm. Partly sunny, with a high near 78. East southeast wind around 6 mph. Chance of precipitation is 20%.
Mostly Sunny
then Slight
Chance
T-storms
 Saturday
Night
Saturday Night: A 50 percent chance of showers and thunderstorms before midnight. Mostly cloudy, with a low around 47. Southeast wind around 7 mph becoming west after midnight.
Chance
T-storms then
Mostly Cloudy
 Sunday

Sunday: A 20 percent chance of showers and thunderstorms after noon. Mostly sunny, with a high near 69. West wind 10 to 13 mph, with gusts as high as 22 mph.
Partly Sunny
then Slight
Chance
T-storms
 Sunday
Night
Sunday Night: A slight chance of showers and thunderstorms, then a chance of showers after midnight. Mostly cloudy, with a low around 41. West wind 5 to 11 mph, with gusts as high as 21 mph. Chance of precipitation is 40%.
Slight Chance
T-storms then
Chance
Showers
 Monday

Monday: A chance of showers, with thunderstorms also possible after noon. Partly sunny, with a high near 64. West wind 6 to 11 mph, with gusts as high as 21 mph.
Chance
Showers then
Slight Chance
T-storms
 Monday
Night
Monday Night: Mostly clear, with a low around 40.
Mostly Clear
Lo 39 °F Hi 70 °F Lo 45 °F Hi 78 °F Lo 47 °F Hi 69 °F Lo 41 °F Hi 64 °F Lo 40 °F

 

Tonight
 
 Partly cloudy, with a low around 39. Northwest wind around 6 mph becoming calm in the evening.
Juneteenth
 
 Mostly sunny, with a high near 70. Calm wind becoming east 5 to 8 mph in the afternoon.
Friday Night
 
 Mostly cloudy, with a low around 45. East southeast wind 8 to 15 mph, with gusts as high as 26 mph.
Saturday
 
 A slight chance of showers between noon and 3pm, then a slight chance of showers and thunderstorms after 3pm. Partly sunny, with a high near 78. East southeast wind around 6 mph. Chance of precipitation is 20%.
Saturday Night
 
 A 50 percent chance of showers and thunderstorms before midnight. Mostly cloudy, with a low around 47. Southeast wind around 7 mph becoming west after midnight.
Sunday
 
 A 20 percent chance of showers and thunderstorms after noon. Mostly sunny, with a high near 69. West wind 10 to 13 mph, with gusts as high as 22 mph.
Sunday Night
 
 A slight chance of showers and thunderstorms, then a chance of showers after midnight. Mostly cloudy, with a low around 41. West wind 5 to 11 mph, with gusts as high as 21 mph. Chance of precipitation is 40%.
Monday
 
 A chance of showers, with thunderstorms also possible after noon. Partly sunny, with a high near 64. West wind 6 to 11 mph, with gusts as high as 21 mph.
Monday Night
 
 Mostly clear, with a low around 40.
Tuesday
 
 Sunny, with a high near 72.
Tuesday Night
 
 Mostly clear, with a low around 44.
Wednesday
 
 A slight chance of showers and thunderstorms. Mostly sunny, with a high near 79.
Wednesday Night
 
 A slight chance of showers and thunderstorms. Partly cloudy, with a low around 47.
Thursday
 
 A slight chance of showers and thunderstorms. Mostly sunny, with a high near 82.

 

Forecast from NOAA-NWS for Lewistown MT.