December in Ajax 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 Ajax is June–September.
Based on OSHAWA WPCP, ON CA (16.1km), 1995–2024. 20 years of December data.