December in Belfast averages a daily high of 8.5°C with nights around 2.9°C. Expect roughly 18.3 wet days totalling 94.4mm. A hard month to visit for comfort alone.
Across the year, the best time to visit Belfast is June–September.
Based on STORMONT CASTLE, UK (6.3km), 1995–2024. 25 years of December data.