May in Sarnia averages a daily high of 19.4°C with nights around 8.9°C. Expect roughly 12.7 wet days totalling 86.1mm. Generally workable, with some weather to plan around.
Across the year, the best time to visit Sarnia is May–September.
Based on PORT HURON, MI US (1.3km), 1995–2024. 28 years of May data.