May in Ontario averages a daily high of 26.2°C with nights around 13.1°C. Rain is rare — about 1.6 wet days and 7.4mm across the month. Comfortable conditions for being outdoors all day.
Across the year, the best time to visit Ontario is March–May.
Based on ONTARIO INTERNATIONAL AIRPORT, CA US (6.9km), 1995–2024. 26 years of May data.