December in Sarnia averages a daily high of 2.4°C with nights around -3.5°C. Expect roughly 12.7 wet days totalling 61mm. A hard month to visit for comfort alone.
Across the year, the best time to visit Sarnia is May–September.
Based on PORT HURON, MI US (1.3km), 1995–2024. 27 years of December data.