May Weather in Ontario, United States

Last updated: June 24, 2025

In Ontario, United States, the average temperature in May hovers around 15°C (59°F), making it a comfortable time to visit. However, be prepared for a range of temperatures, with minimums dropping to -1°C (31°F) and occasional highs reaching 34°C (94°F). Expect about 141 mm (5.5 in) of precipitation spread over 15 days, contributing to an average humidity level of around 75%. Whether you're planning outdoor activities or sightseeing, these conditions set the stage for a memorable experience!

May Temperature in Ontario

In May in Ontario, the average temperature is 15°C (59°F). Maximums can reach 34°C (94°F), while minimums can drop to as low as -1°C (31°F). Therefore, travelers should be prepared for a wide range of temperatures and pack accordingly.

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 15°C (59°F), with highs reaching up to 34°C (94°F) and lows dropping to around -1°C (31°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 total precipitation amount is 141 mm (5.5 in) over the course of 15 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 141 mm (5.5 inches) of precipitation spread over approximately 15 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 75%. With an average temperature of 15°C (59°F), this humidity feels like a warm blanket enveloping you, making it feel more oppressive than refreshing, which can be a challenge for travelers seeking comfort while exploring the area.

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 75%, 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 is 9, which corresponds to a very high Exposure Category. The time to burn is just 15 minutes, so it's essential to take precautions. For 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 9, 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	-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