May in Ajax averages a daily high of 17.6°C with nights around 8°C. Expect roughly 11.3 wet days totalling 87.8mm. Generally workable, with some weather to plan around.
Across the year, the best time to visit Ajax is June–September.
Based on OSHAWA WPCP, ON CA (16.1km), 1995–2024. 23 years of May data.