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The temperatures in Idaho 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 Idaho 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 Idaho in September 2025.
If you’re planning to visit Idaho in the near future, we highly recommend that you review the 14 day weather forecast for Idaho before you arrive.
| Month | Temperatures | Rainy Days | Dry Days | Snowy Days | Rainfall | Weather | More details |
|---|---|---|---|---|---|---|---|
| January | -15° / -22° | 1 | 23 | 7 | 3 mm | Awful | Idaho in January |
| February | -11° / -19° | 2 | 19 | 7 | 6 mm | Awful | Idaho in February |
| March | 0° / -9° | 3 | 20 | 8 | 10 mm | Awful | Idaho in March |
| April | 11° / 1° | 1 | 25 | 3 | 22 mm | Bad | Idaho in April |
| May | 19° / 8° | 4 | 27 | 1 | 44 mm | Good | Idaho in May |
| June | 24° / 15° | 5 | 25 | 0 | 60 mm | Perfect | Idaho in June |
| July | 27° / 18° | 5 | 26 | 0 | 84 mm | Perfect | Idaho in July |
| August | 25° / 16° | 3 | 28 | 0 | 57 mm | Perfect | Idaho in August |
| September | 19° / 9° | 4 | 26 | 0 | 37 mm | Good | Idaho in September |
| October | 9° / 1° | 2 | 26 | 3 | 24 mm | Bad | Idaho in October |
| November | -3° / -9° | 2 | 21 | 8 | 12 mm | Awful | Idaho in November |
| December | -13° / -19° | 1 | 22 | 7 | 4 mm | Awful | Idaho in December |