December in Vacaville averages a daily high of 14.3°C with nights around 3.3°C. Expect roughly 10.4 wet days totalling 125.7mm. Generally workable, with some weather to plan around.
Across the year, the best time to visit Vacaville is April–May.
Based on VACAVILLE NUT TREE AIRPORT ASOS, CA US (3.4km), 1995–2024. 27 years of December data.