May Weather in Ontario, United States

Last updated: June 24, 2025

In Ontario, United States, the average temperature in May hovers around 17°C (64°F), offering a comfortable climate. However, temperatures can swing from a chilly 2°C (36°F) to a sizzling 37°C (100°F). Expect about 28 mm (1.1 in) of precipitation spread over 5 days, while the average humidity sits at a refreshing 71%.

May Temperature in Ontario

In May in Ontario, the average temperature is 17°C (64°F). Maximums can reach 37°C (100°F), while minimums can drop as low as 2°C (36°F). Travelers can expect a wide range of temperatures, so it's advisable to pack both light clothing for the heat and warmer layers for the cooler nights.

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

The chart illustrates May 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, May typically has an average temperature of 17°C (64°F), with highs reaching up to 37°C (100°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.

May Precipitation in Ontario

In Ontario in May, the precipitation amount is 28 mm (1.1 in) over a period of 5 days.

May Precipitation Trends in Ontario

The chart displays monthly precipitation patterns in Ontario, with values for each month alongside May’s data, which is highlighted for easy comparison. It shows the amount of precipitation, providing insights into how May’s conditions compare to those of other months. In Ontario, May typically receives around 28 mm (1.1 inches) of precipitation spread over approximately 5 days.

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

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Millimeters (mm) Inches (in)

May Humidity in Ontario

In Ontario in May humidity is 71%. With an average temperature of 17°C (64°F), this humidity feels like a warm, enveloping embrace that can make travel feel a bit sticky, yet still pleasant as you explore the sights with a gentle sheen of perspiration.

May Average Humidity in Ontario

This chart illustrates the average monthly humidity levels in Ontario, with May’s data highlighted for easy comparison. It shows the fluctuation in humidity throughout the year, helping you understand how conditions vary by season. In May, average humidity in Ontario is approximately 71%, offering insight into how humid the weather typically is during this month.

Data source: Humidity data for May generated using information from the Copernicus Climate Change Service.

May UV Index in Ontario

In Ontario in May, the maximum UV index reaches 10, which corresponds to a very high Exposure Category. With a time to burn of just 15 minutes, it's crucial to take precautions. For more detailed information, you can check the Hourly UV Index in Ontario.

Maximum UV Index Levels in Ontario for May

The chart shows the monthly maximum UV Index (UVI) for Ontario in May, 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 May, the maximum UV index in Ontario typically reaches 10, which falls under the very high exposure category.

Data source: Ontario May 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 May 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 May’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 May’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