December in Mainz averages a daily high of 5.2°C with nights around 0.9°C. Expect roughly 13.1 wet days totalling 51.3mm. A hard month to visit for comfort alone.
Across the year, the best time to visit Mainz is May–September.
Based on MAINZ LERCHENBERG ZDF, GM (5.1km), 1995–2024. 29 years of December data.