July in Sarnia averages a daily high of 27.7°C with nights around 18.1°C. Expect roughly 10.1 wet days totalling 85.7mm. Comfortable conditions for being outdoors all day.
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 July data.