May in Ottawa averages a daily high of 19.7°C with nights around 8.3°C. Expect roughly 12.6 wet days totalling 78.2mm. Generally workable, with some weather to plan around.
Across the year, the best time to visit Ottawa is May–September.
Based on OTTAWA CDA, ON CA (3.4km), 1995–2024. 28 years of May data.