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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 20°C (67°F). Visitors can expect a minimum of only 4°C (40°F) and a maximum of 33°C (91°F), making it a month of varied weather. During this time, expect approximately 80 mm (3.2 in) of precipitation spread over 10 days. With an average humidity of 78%, it's the perfect opportunity to experience the environment's lush richness!

September Temperature in Ontario

In September, in Ontario, the average temperature is 20°C (67°F). The maximum can reach 33°C (91°F) and the minimum can be as low as 4°C (40°F). This range makes Ontario a versatile destination for travelers, offering comfortable weather for both outdoor adventures and relaxing getaways.

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 20°C (67°F), with highs reaching up to 33°C (91°F) and lows dropping to around 4°C (40°F).
JanFebMarAprMayJunJulAugSepOctNovDec293240506270747267564135
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 is 80 mm (3.2 in) over a span of 10 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 80 mm (3.2 inches) of precipitation spread over approximately 10 days.
JanFebMarAprMayJunJulAugSepOctNovDec81981031301261411238980989292
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 20°C (67°F), this humidity feels like walking through a warm, thick blanket, making travel a bit sticky and requiring frequent breaks to find shade and cool refreshments.

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.
JanFebMarAprMayJunJulAugSepOctNovDec88%87%87%88%81%82%81%78%78%82%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 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 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 8, which falls under the very high exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec356810101098642
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)81 mm (3.2 inches)88%moderate
February Weather0°C (32°F)98 mm (3.8 inches)87%moderate
March Weather5°C (40°F)103 mm (4.1 inches)87%high
April Weather10°C (50°F)130 mm (5.1 inches)87%very high
May Weather17°C (62°F)126 mm (5.0 inches)81%very high
June Weather21°C (71°F)141 mm (5.5 inches)82%very high
July Weather24°C (75°F)123 mm (4.8 inches)81%very high
August Weather22°C (72°F)89 mm (3.5 inches)78%very high
September Weather20°C (67°F)80 mm (3.2 inches)78%very high
October Weather14°C (57°F)98 mm (3.9 inches)82%high
November Weather5°C (41°F)92 mm (3.6 inches)89%moderate
December Weather1°C (35°F)92 mm (3.6 inches)86%low

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