Last updated: June 24, 2025
In September, the average temperature in Ottawa, United States hovers around 20°C (69°F), making it quite pleasant. However, be prepared for temperature fluctuations, with lows dipping to 4°C (39°F) and highs reaching up to 35°C (95°F). During this month, 91 mm (3.6 in) of precipitation is recorded over approximately 9 days, contributing to an average humidity level of 80%. Whether you're seeking warmth or a refreshing drizzle, this month offers a unique climate experience!
In September in Ottawa, the average temperature is 20°C (69°F), with maximums reaching up to 35°C (95°F) and minimums dropping as low as 4°C (39°F). This climate makes Ottawa an ideal destination for travelers seeking a pleasant mix of warmth and cooler evenings.
In Ottawa in September, the precipitation amount is 91 mm (3.6 in) spread over 9 days.
In Ottawa in September, humidity is 80%. With an average temperature of 20°C (69°F), this humidity feels like a warm blanket enveloping you, making every step slightly more challenging as you navigate the air that clings to your skin, often leaving you longing for a cool breeze while exploring the sights.
In Ottawa in September, the maximum UV index is 8, which corresponds to a very high Exposure Category. This means that the time to burn is only 15 minutes. For more detailed information, you can refer to the Hourly UV Index in Ottawa.
UV Risk Categories
Weather in Ottawa varies notably across the year, with each month offering distinct climate conditions. This page compares September’s weather to other months in Ottawa, focusing on differences in temperature, rainfall, humidity, and UV levels.
| Temperature | Precipitation | Humidity | UV | |
|---|---|---|---|---|
| January Weather | -3°C (26°F) | 62 mm (2.5 inches) | 82% | moderate |
| February Weather | -2°C (28°F) | 66 mm (2.6 inches) | 83% | moderate |
| March Weather | 5°C (41°F) | 93 mm (3.7 inches) | 84% | high |
| April Weather | 10°C (50°F) | 117 mm (4.6 inches) | 85% | very high |
| May Weather | 17°C (63°F) | 165 mm (6.5 inches) | 79% | very high |
| June Weather | 23°C (73°F) | 145 mm (5.7 inches) | 82% | very high |
| July Weather | 24°C (76°F) | 101 mm (4.0 inches) | 80% | very high |
| August Weather | 23°C (74°F) | 87 mm (3.4 inches) | 81% | very high |
| September Weather | 20°C (69°F) | 91 mm (3.6 inches) | 80% | very high |
| October Weather | 13°C (56°F) | 134 mm (5.3 inches) | 82% | high |
| November Weather | 4°C (40°F) | 57 mm (2.2 inches) | 88% | moderate |
| December Weather | 1°C (34°F) | 55 mm (2.2 inches) | 84% | low |