December in St. Catharines averages a daily high of 3.8°C with nights around -1.1°C. Expect roughly 11.2 wet days totalling 48mm. A hard month to visit for comfort alone.
Across the year, the best time to visit St. Catharines is June–September.
Based on PORT WELLER AUT, ON CA (9km), 1995–2024. 26 years of December data.