December in Ottawa averages a daily high of -1.2°C with nights around -8.1°C. Expect roughly 14.9 wet days totalling 76.9mm. A hard month to visit for comfort alone.
Across the year, the best time to visit Ottawa is May–September.
Based on OTTAWA CDA, ON CA (3.4km), 1995–2024. 29 years of December data.