In December, Castro Valley typically sees daytime highs of 13.2°C and overnight lows around 5.1°C. Compared to the annual average high of 20.0°C, December runs -6.8°C.
December in Castro Valley averages a daytime high of 13.2°C and an overnight low of 5.1°C.
December runs -6.8°C compared to Castro Valley's annual average high of 20.0°C, ranking #11 of 12 months by warmth.
Plan for daytime highs near 13.2°C and cooler evenings around 5.1°C.