Ottawa weather in September
September in Ottawa: nice, a little rain, with clean air — one of the best months to visit.
#2 of 12 months in Ottawa · #216 of 897 destinations to visit in September · comfort 89/100 (tier A)
Updated June 2026 · climate normals from ERA5 reanalysis
Traveller notes on Ottawa in September
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Ottawa climate normals — September
| Daytime high | 21°C / 70°F | 😎 nice |
|---|---|---|
| Nighttime low | 13°C / 55°F | |
| Rainfall | 73 mm / 2.9 in | 🌦 some rain |
| Rainy days | 9 days | |
| Humidity | 76% | 💦 very humid |
| Dew point | 12°C / 54°F | |
| Sunshine | 8.9 h/day | |
| Daylight | 12.5 h | |
| Wind | 14 km/h / 9 mph | |
| Air quality (US AQI) | 39 | 🍃 good |
Monthly averages from ERA5 reanalysis. AQI is the mean US Air Quality Index for the month.
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Ottawa in September — FAQ
- Is September a good time to visit Ottawa?
- September in Ottawa: nice, a little rain, with clean air — one of the best months to visit. It ranks #2 of 12 months for Ottawa on SeasonMap's comfort score (89/100).
- What is the weather like in Ottawa in September?
- In September, Ottawa averages a daily high of 20.9°C and a low of 12.7°C, with about 72.6 mm of rain over roughly 9.4 rainy days.
- What is the air quality in Ottawa in September?
- Ottawa has a mean US Air Quality Index of about 39 in September.