December in Riverside averages a daily high of 20.6°C with nights around 5.6°C. Expect roughly 3.7 wet days totalling 33.5mm. Comfortable conditions for being outdoors all day.
Across the year, the best time to visit Riverside is October–May.
Based on RIVERSIDE FIRE STATION 3, CA US (0.8km), 1995–2024. 16 years of December data.