May in Thornhill averages a daily high of 19.7°C with nights around 7.7°C. Expect roughly 11.3 wet days totalling 80.7mm. Comfortable conditions for being outdoors all day.
Across the year, the best time to visit Thornhill is May–September.
Based on TORONTO NORTH YORK, ON CA (4.9km), 1995–2024. 28 years of May data.