December in Vallejo averages a daily high of 14.3°C with nights around 5.6°C. Expect roughly 8.9 wet days totalling 81.3mm. Generally workable, with some weather to plan around.
Across the year, the best time to visit Vallejo is April–June.
Based on VALLEJO, CA US (6.1km), 1995–2024. 10 years of December data.