December in Heerlen averages a daily high of 6.4°C with nights around 1.6°C. Expect roughly 17.3 wet days totalling 71mm. A hard month to visit for comfort alone.
Across the year, the best time to visit Heerlen is May–September.
Based on MAASTRICHT, NL (15.6km), 1995–2024. 30 years of December data.