December in Hayward averages a daily high of 14.9°C with nights around 6.4°C. Expect roughly 10.6 wet days totalling 88mm. Generally workable, with some weather to plan around.
Across the year, the best time to visit Hayward is May–October.
Based on HAYWARD AIR TERMINAL, CA US (3.7km), 1995–2024. 27 years of December data.