September Weather in Ontario, United States

Last updated: June 24, 2025

In Ontario, United States, the average temperature in September hovers around 21°C (70°F). Visitors can experience a range of temperatures, with a minimum of 5°C (42°F) and a maximum of 41°C (106°F). The region receives approximately 10 mm (0.4 in) of precipitation spread over 2 days, while the average humidity stands at a comfortable 48%. Whether you're enjoying sunny days or light showers, Ontario offers a diverse climate for every traveler!

September Temperature in Ontario

In September in Ontario, the average temperature is 21°C (70°F). Maximums can reach 41°C (106°F), and minimums can be as low as 5°C (42°F). This makes it essential for travelers to pack accordingly, blending light layers for warm days and warmer clothing for cooler evenings.

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 21°C (70°F), with highs reaching up to 41°C (106°F) and lows dropping to around 5°C (42°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 precipitation amount is 10 mm (0.4 in) over a period of 2 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 10 mm (0.4 inches) of precipitation spread over approximately 2 days.

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

Choose your preferred precipitation unit

Millimeters (mm) Inches (in)

September Humidity in Ontario

In Ontario in September humidity is 48%. With an average temperature of 21°C (70°F), this humidity feels like a pleasant and mild embrace, making it comfortable for traveling and exploring the area.

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 48%, 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	0°C (33°F)	42 mm (1.7 inches)	88%	moderate
February Weather	2°C (36°F)	46 mm (1.8 inches)	89%	moderate
March Weather	8°C (47°F)	32 mm (1.3 inches)	85%	high
April Weather	12°C (55°F)	23 mm (0.9 inches)	79%	high
May Weather	17°C (64°F)	28 mm (1.1 inches)	71%	very high
June Weather	23°C (73°F)	16 mm (0.6 inches)	71%	extreme
July Weather	29°C (84°F)	1 mm (0.0 inches)	66%	very high
August Weather	27°C (82°F)	5 mm (0.2 inches)	50%	very high
September Weather	21°C (70°F)	10 mm (0.4 inches)	48%	very high
October Weather	12°C (55°F)	16 mm (0.6 inches)	65%	moderate
November Weather	6°C (43°F)	27 mm (1.1 inches)	84%	moderate
December Weather	1°C (35°F)	29 mm (1.1 inches)	87%	low