September Weather in Ontario, United States

Last updated: June 24, 2025

In Ontario, United States, the average temperature in September hovers around 18°C (64°F), providing a comfortable climate for outdoor activities. Expect a minimum of 2°C (36°F) and a maximum of 33°C (92°F), showcasing considerable variability. With 112 mm (4.4 in) of precipitation spread over 10 days, be prepared for occasional showers. The average humidity levels around 74% ensure a moist atmosphere, enhancing the overall experience of this enchanting location.

September Temperature in Ontario

In September in Ontario, the average temperature is 18°C (64°F), with maximums reaching 33°C (92°F) and minimums dropping as low as 2°C (36°F). This diverse temperature range makes Ontario an ideal destination for travelers seeking both warm and cooler experiences during their visit.

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 18°C (64°F), with highs reaching up to 33°C (92°F) and lows dropping to around 2°C (36°F).

Data source: Temperature data for Ontario generated using information from the Copernicus Climate Change Service.

September Precipitation in Ontario

In Ontario in September, the total precipitation amount is 112 mm (4.4 in) over the course 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 112 mm (4.4 inches) of precipitation spread over approximately 10 days.

Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.

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Millimeters (mm) Inches (in)

September Humidity in Ontario

In Ontario in September humidity is 74%. With an average temperature of 18°C (64°F), this humidity feels like a warm embrace, making it ideal for leisurely strolls but potentially uncomfortable for extended outdoor activities.

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 74%, offering insight into how humid the weather typically is during this month.

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.

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.
	Temperature	Precipitation	Humidity	UV
January Weather	-7°C (20°F)	40 mm (1.6 inches)	84%	low
February Weather	-6°C (21°F)	54 mm (2.1 inches)	85%	moderate
March Weather	2°C (35°F)	59 mm (2.3 inches)	84%	moderate
April Weather	7°C (45°F)	91 mm (3.6 inches)	83%	very high
May Weather	15°C (59°F)	141 mm (5.5 inches)	75%	very high
June Weather	21°C (70°F)	121 mm (4.8 inches)	79%	very high
July Weather	23°C (74°F)	110 mm (4.3 inches)	75%	very high
August Weather	21°C (70°F)	117 mm (4.6 inches)	69%	very high
September Weather	18°C (64°F)	112 mm (4.4 inches)	74%	very high
October Weather	10°C (50°F)	115 mm (4.5 inches)	79%	moderate
November Weather	2°C (35°F)	52 mm (2.0 inches)	88%	moderate
December Weather	-3°C (27°F)	46 mm (1.8 inches)	82%	low