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May Weather in Ontario, United States

Last updated: June 24, 2025

In May, the average temperature in Ontario, United States is a comfortable 12°C (54°F). However, it can drop as low as 0°C (32°F) and rise to a maximum of 25°C (78°F). Visitors can expect about 110 mm (4.3 in) of precipitation over 13 days, and the atmosphere is typically humid with an average humidity of 82%.

May Temperature in Ontario

In May in Ontario, the average temperature is 12°C (54°F). The maximum can reach 25°C (78°F), while the minimum can dip as low as 0°C (32°F). This variation makes it a great time for travelers to enjoy a mix of mild days and cooler evenings, perfect for exploring outdoor activities and local attractions.

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 12°C (54°F), with highs reaching up to 25°C (78°F) and lows dropping to around 0°C (32°F).
JanFebMarAprMayJunJulAugSepOctNovDec283035445364727266554134
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.

May Precipitation in Ontario

In Ontario in May, the total precipitation amount is 110 mm (4.3 in) over the course of 13 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 110 mm (4.3 inches) of precipitation spread over approximately 13 days.
JanFebMarAprMayJunJulAugSepOctNovDec9494851241108014910383164110113
Data source: Precipitation data for May generated using information from the Copernicus Climate Change Service.
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May Humidity in Ontario

In Ontario in May humidity is 82%. With an average temperature of 12°C (54°F), this humidity feels like a heavy blanket wrapping around you, making every step feel sluggish and sweat-inducing, which can be quite uncomfortable for traveling.

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 82%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec90%90%87%88%82%79%78%76%78%84%89%86%
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.
JanFebMarAprMayJunJulAugSepOctNovDec24681010997532
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.
 TemperaturePrecipitationHumidityUV
January Weather-2°C (29°F)94 mm (3.7 inches)90%low
February Weather-1°C (30°F)94 mm (3.7 inches)90%moderate
March Weather2°C (35°F)85 mm (3.3 inches)87%high
April Weather6°C (44°F)124 mm (4.9 inches)88%very high
May Weather12°C (54°F)110 mm (4.3 inches)82%very high
June Weather18°C (64°F)80 mm (3.1 inches)79%very high
July Weather22°C (72°F)149 mm (5.9 inches)78%very high
August Weather22°C (72°F)103 mm (4.1 inches)76%very high
September Weather19°C (66°F)83 mm (3.3 inches)78%high
October Weather13°C (56°F)164 mm (6.5 inches)84%moderate
November Weather5°C (42°F)110 mm (4.3 inches)89%moderate
December Weather1°C (34°F)113 mm (4.4 inches)86%low

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