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September Weather in Ontario, United States

Last updated: June 24, 2025

In September, the average temperature in Ontario, United States is a pleasant 19°C (66°F). However, be prepared for a bit of a range, with temperatures dipping to a minimum of 7°C (44°F) and reaching up to 30°C (87°F). You can expect 83 mm (3.3 in) of precipitation spread over about 8 days, accompanied by an average humidity level of 78%.

September Temperature in Ontario

In September in Ontario, the average temperature is 19°C (66°F). The maximum can reach 30°C (87°F), while the minimum can be as low as 7°C (44°F). This makes Ontario a comfortable destination for travelers seeking pleasant weather and a range of outdoor activities.

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

The chart illustrates September temperature patterns in Ontario, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Ontario, September typically has an average temperature of 19°C (66°F), with highs reaching up to 30°C (87°F) and lows dropping to around 7°C (44°F).
JanFebMarAprMayJunJulAugSepOctNovDec283035445364727266554134
Data source: Temperature data for Ontario 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 Ontario

In Ontario in September, the precipitation amount reaches 83 mm (3.3 in) over the course of 8 days.

September Precipitation Trends in Ontario

The chart displays monthly precipitation patterns in Ontario, 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 Ontario, September typically receives around 83 mm (3.3 inches) of precipitation spread over approximately 8 days.
JanFebMarAprMayJunJulAugSepOctNovDec9494851241108014910383164110113
Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.
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September Humidity in Ontario

In Ontario in September, humidity is 78%. With an average temperature of 19°C (66°F), this humidity feels like a warm, enveloping blanket, making traveling quite uncomfortable unless you're well-prepared with lightweight, breathable clothing and frequent breaks to stay hydrated.

September Average Humidity in Ontario

This chart illustrates the average monthly humidity levels in Ontario, 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 Ontario is approximately 78%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec90%90%87%88%82%79%78%76%78%84%89%86%
Data source: Humidity data for September generated using information from the Copernicus Climate Change Service.

September UV Index in Ontario

In Ontario in September, the maximum UV index is 7, which corresponds to the high Exposure Category. This means that the time to burn is approximately 25 minutes. For more detailed information, you can check the Hourly UV Index in Ontario.

Maximum UV Index Levels in Ontario for September

The chart shows the monthly maximum UV Index (UVI) for Ontario 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 Ontario typically reaches 7, which falls under the high exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec24681010997532
Data source: Ontario 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 Ontario Compares to Other Months

Weather in Ontario varies notably across the year, with each month offering distinct climate conditions. This page compares September’s weather to other months in Ontario, focusing on differences in temperature, rainfall, humidity, and UV levels.

This table compares monthly weather conditions in Ontario, showing how September’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
 TemperaturePrecipitationHumidityUV
January Weather-2°C (29°F)94 mm (3.7 inches)90%low
February Weather-1°C (30°F)94 mm (3.7 inches)90%moderate
March Weather2°C (35°F)85 mm (3.3 inches)87%high
April Weather6°C (44°F)124 mm (4.9 inches)88%very high
May Weather12°C (54°F)110 mm (4.3 inches)82%very high
June Weather18°C (64°F)80 mm (3.1 inches)79%very high
July Weather22°C (72°F)149 mm (5.9 inches)78%very high
August Weather22°C (72°F)103 mm (4.1 inches)76%very high
September Weather19°C (66°F)83 mm (3.3 inches)78%high
October Weather13°C (56°F)164 mm (6.5 inches)84%moderate
November Weather5°C (42°F)110 mm (4.3 inches)89%moderate
December Weather1°C (34°F)113 mm (4.4 inches)86%low

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