Click on a day for an hourly weather forecast
The temperatures in Ottawa in September are comfortable with low of 10°C and and high up to 21°C.
You can expect about 3 to 8 days of rain in Ottawa 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 Ottawa in September 2025.
If you’re planning to visit Ottawa in the near future, we highly recommend that you review the 14 day weather forecast for Ottawa before you arrive.
| Month | Temperatures | Rainy Days | Dry Days | Snowy Days | Rainfall | Weather | More details |
|---|---|---|---|---|---|---|---|
| January | -7° / -14° | 5 | 5 | 22 | 89 mm | Awful | Ottawa in January |
| February | -5° / -13° | 5 | 3 | 21 | 85 mm | Awful | Ottawa in February |
| March | 1° / -6° | 8 | 8 | 16 | 85 mm | Awful | Ottawa in March |
| April | 9° / 1° | 11 | 13 | 7 | 122 mm | Awful | Ottawa in April |
| May | 18° / 8° | 8 | 23 | 1 | 116 mm | Ok | Ottawa in May |
| June | 22° / 12° | 7 | 23 | 0 | 129 mm | Ok | Ottawa in June |
| July | 25° / 15° | 6 | 25 | 0 | 129 mm | Perfect | Ottawa in July |
| August | 25° / 15° | 7 | 24 | 0 | 137 mm | Good | Ottawa in August |
| September | 21° / 10° | 5 | 25 | 0 | 102 mm | Good | Ottawa in September |
| October | 13° / 5° | 9 | 21 | 1 | 134 mm | Bad | Ottawa in October |
| November | 5° / -2° | 7 | 14 | 8 | 80 mm | Awful | Ottawa in November |
| December | -2° / -8° | 7 | 6 | 18 | 101 mm | Awful | Ottawa in December |