December in Lake Forest averages a daily high of 20.3°C with nights around 8.5°C. Expect roughly 4.2 wet days totalling 64.4mm. Comfortable conditions for being outdoors all day.
Across the year, the best time to visit Lake Forest is October–June.
Based on IRVINE RANCH, CA US (8.7km), 1995–2024. 20 years of December data.