December in Rosemead averages a daily high of 20.8°C with nights around 6.7°C. Expect roughly 5 wet days totalling 48.2mm. Comfortable conditions for being outdoors all day.
Across the year, the best time to visit Rosemead is March–June.
Based on SAN GABRIEL FIRE DEPARTMENT, CA US (2.6km), 1995–2024. 13 years of December data.