December in Petaluma averages a daily high of 14.7°C with nights around 4°C. Expect roughly 12.7 wet days totalling 140.1mm. Generally workable, with some weather to plan around.
Across the year, the best time to visit Petaluma is May–October.
Based on PETALUMA AIRPORT, CA US (3.8km), 1995–2024. 25 years of December data.