Click on a day for an hourly weather forecast
The temperatures in Boise in September are quite cold with temperatures between 9°C and 19°C, warm clothes are a must.
You can expect about 3 to 8 days of rain in Boise during the month of September. It’s a good idea to bring along your umbrella so that you don’t get caught in poor weather.
Our weather forecast can give you a great sense of what weather to expect in Boise in September 2025.
If you’re planning to visit Boise in the near future, we highly recommend that you review the 14 day weather forecast for Boise before you arrive.
| Month | Temperatures | Rainy Days | Dry Days | Snowy Days | Rainfall | Weather | More details |
|---|---|---|---|---|---|---|---|
| January | -15° / -22° | 1 | 23 | 7 | 3 mm | Awful | Boise in January |
| February | -11° / -19° | 2 | 19 | 7 | 6 mm | Awful | Boise in February |
| March | 0° / -9° | 3 | 20 | 8 | 10 mm | Awful | Boise in March |
| April | 11° / 1° | 1 | 25 | 3 | 22 mm | Bad | Boise in April |
| May | 19° / 8° | 4 | 27 | 1 | 44 mm | Good | Boise in May |
| June | 24° / 15° | 5 | 25 | 0 | 60 mm | Perfect | Boise in June |
| July | 27° / 18° | 5 | 26 | 0 | 84 mm | Perfect | Boise in July |
| August | 25° / 16° | 3 | 28 | 0 | 57 mm | Perfect | Boise in August |
| September | 19° / 9° | 4 | 26 | 0 | 37 mm | Good | Boise in September |
| October | 9° / 1° | 2 | 26 | 3 | 24 mm | Bad | Boise in October |
| November | -3° / -9° | 2 | 21 | 8 | 12 mm | Awful | Boise in November |
| December | -13° / -19° | 1 | 22 | 7 | 4 mm | Awful | Boise in December |