Click on a day for an hourly weather forecast
The temperatures in Great Falls in September are comfortable with low of 10°C and and high up to 23°C.
The wather in Great Falls in September can vary between cold and nice weather days. Expect a few rainy days but usually not more than 3.
Please note that Great Falls can expect a few days of snow in September.
Our weather forecast can give you a great sense of what weather to expect in Great Falls in September 2025.
If you’re planning to visit Great Falls in the near future, we highly recommend that you review the 14 day weather forecast for Great Falls before you arrive.
| Month | Temperatures | Rainy Days | Dry Days | Snowy Days | Rainfall | Weather | More details |
|---|---|---|---|---|---|---|---|
| January | 0° / -7° | 3 | 16 | 12 | 19 mm | Awful | Great Falls in January |
| February | 0° / -8° | 3 | 11 | 15 | 23 mm | Awful | Great Falls in February |
| March | 7° / -3° | 3 | 17 | 11 | 25 mm | Bad | Great Falls in March |
| April | 11° / 1° | 4 | 19 | 7 | 46 mm | Bad | Great Falls in April |
| May | 17° / 5° | 5 | 24 | 2 | 53 mm | Ok | Great Falls in May |
| June | 23° / 9° | 4 | 26 | 0 | 49 mm | Perfect | Great Falls in June |
| July | 29° / 14° | 1 | 30 | 0 | 16 mm | Good | Great Falls in July |
| August | 28° / 14° | 1 | 30 | 0 | 27 mm | Perfect | Great Falls in August |
| September | 23° / 10° | 2 | 28 | 1 | 20 mm | Perfect | Great Falls in September |
| October | 13° / 3° | 3 | 24 | 4 | 30 mm | Bad | Great Falls in October |
| November | 6° / -2° | 3 | 19 | 9 | 20 mm | Awful | Great Falls in November |
| December | -1° / -8° | 2 | 15 | 13 | 18 mm | Awful | Great Falls in December |