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September Weather in Ottawa, United States

Last updated: June 24, 2025

In September, the average temperature in Ottawa, United States is a pleasant 22°C (73°F). Expect a range where the minimum can dip to 5°C (41°F) and the maximum can soar up to 34°C (93°F). You'll also experience 81 mm (3.2 in) of precipitation spread over 8 days, with an average humidity of 71% making the air feel quite comfortable.

September Temperature in Ottawa

In September in Ottawa, the average temperature is 22°C (73°F). Maximums can reach 34°C (93°F), while minimums can drop to as low as 5°C (41°F). This makes Ottawa an ideal destination for travelers seeking a mix of warm and cool weather experiences.

September Weather in Ottawa: Daily Temperature Highs, Lows, and Averages

The chart illustrates September temperature patterns in Ottawa, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Ottawa, September typically has an average temperature of 22°C (73°F), with highs reaching up to 34°C (93°F) and lows dropping to around 5°C (41°F).
JanFebMarAprMayJunJulAugSepOctNovDec333447556677807772584539
Data source: Temperature data for Ottawa generated using information from the Copernicus Climate Change Service.
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The average of daily temperatures (24 hours) calculated across all days in the month.

September Precipitation in Ottawa

In Ottawa in September, the precipitation amount is 81 mm (3.2 in) over the course of 8 days.

September Precipitation Trends in Ottawa

The chart displays monthly precipitation patterns in Ottawa, with values for each month alongside September’s data, which is highlighted for easy comparison. It shows the amount of precipitation, providing insights into how September’s conditions compare to those of other months. In Ottawa, September typically receives around 81 mm (3.2 inches) of precipitation spread over approximately 8 days.
JanFebMarAprMayJunJulAugSepOctNovDec56369996196109112120811154133
Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.
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September Humidity in Ottawa

In Ottawa in September humidity is 71%. With an average temperature of 22°C (73°F), this humidity feels like a thick, warm blanket wrapping around you, making travel feel a bit sluggish but still pleasant as long as you stay hydrated and take breaks in the shade.

September Average Humidity in Ottawa

This chart illustrates the average monthly humidity levels in Ottawa, with September’s data highlighted for easy comparison. It shows the fluctuation in humidity throughout the year, helping you understand how conditions vary by season. In September, average humidity in Ottawa is approximately 71%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec76%78%70%73%82%82%81%78%71%71%81%84%
Data source: Humidity data for September generated using information from the Copernicus Climate Change Service.

September UV Index in Ottawa

In Ottawa in September, the maximum UV index is 9, which corresponds to a very high Exposure Category. The time to burn is just 15 minutes, so it's essential to take precautions. For detailed information, you can check the Hourly UV Index in Ottawa.

Maximum UV Index Levels in Ottawa for September

The chart shows the monthly maximum UV Index (UVI) for Ottawa in September, representing the highest UV radiation level. The UVI measures the intensity of ultraviolet radiation from the sun, indicating the potential risk of sunburn and UV-related health issues. In September, the maximum UV index in Ottawa typically reaches 9, which falls under the very high exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec3679101111109743
Data source: Ottawa September UVI data generated using information from the Copernicus Climate Change Service.

UV Risk Categories

  •  Extreme (11+): Avoid the sun, stay in shade.
  •  Very High (8-10): Limit sun exposure.
  •  High (6-7): Use SPF 30+ and protective clothing.
  •  Moderate (3-5): Midday shade recommended.
  •  Low (0-2): No protection needed.

How September Weather in Ottawa Compares to Other Months

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.

This table compares monthly weather conditions in Ottawa, showing how September’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
 TemperaturePrecipitationHumidityUV
January Weather0°C (33°F)56 mm (2.2 inches)76%moderate
February Weather1°C (34°F)36 mm (1.4 inches)77%high
March Weather9°C (48°F)98 mm (3.9 inches)70%high
April Weather13°C (55°F)96 mm (3.8 inches)73%very high
May Weather19°C (66°F)196 mm (7.7 inches)82%very high
June Weather25°C (77°F)109 mm (4.3 inches)82%extreme
July Weather27°C (80°F)112 mm (4.4 inches)81%extreme
August Weather25°C (77°F)120 mm (4.7 inches)78%very high
September Weather22°C (73°F)81 mm (3.2 inches)71%very high
October Weather14°C (58°F)115 mm (4.5 inches)71%high
November Weather7°C (45°F)41 mm (1.6 inches)81%moderate
December Weather4°C (39°F)33 mm (1.3 inches)84%moderate

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