December in Oshawa averages a daily high of 2.5°C with nights around -3.8°C. Expect roughly 12.2 wet days totalling 67.6mm. A hard month to visit for comfort alone.
Across the year, the best time to visit Oshawa is June–September.
Based on OSHAWA WPCP, ON CA (3.9km), 1995–2024. 20 years of December data.