December in Helsinki averages a daily high of 1.2°C with nights around -3.3°C. Expect roughly 15.8 wet days totalling 59.5mm. A hard month to visit for comfort alone.
Across the year, the best time to visit Helsinki is June–August.
Based on HELSINKI KAISANIEMI AWS, FI (0.9km), 1995–2024. 30 years of December data.