Castro Valley (CA) Weather & Climate: Best Time to Visit

The weather in Castro Valley changes moderately throughout the year, offering enough variation to appreciate each season. Average maximum daytime temperatures range from a comfortable 25°C (77°F) in September, the warmest time of the year, to a moderate 14°C (57°F) during cooler months like December.

At night, you can expect temperatures ranging from 13°C (55°F) in September to around 5°C (41°F) during December.

Check out our detailed temperature page for more information.

Temperature ranges by month

Generally, Castro Valley experiences moderate precipitation patterns, averaging 512 mm (20 in) yearly. Significant seasonal changes in precipitation occur throughout the year. In the wettest month, December it receives high rainfall, averaging 111 mm (4.4 in) of precipitation, recorded across 13 rainy days. In contrast, the driest month August brings less rainfall, with 0.1 mm (0 in) over 0 rainy days. For more details, please visit our Castro Valley Precipitation page.

The mean monthly precipitation over the year, including rain, hail, and snow

The average number of days each month with precipitation

Seasonal changes in sunshine hours are quite dramatic in Castro Valley. While May receives considerable daily sunshine with up to 10.8 hours, December marks the darkest time of the year, where sunshine is scarce with only 5.3 hours of sunlight per day.

Visit our detailed sunshine hours page for more information.

Monthly hours of sunshine

Daily hours of sunshine

Daily percentage of sunshine

The relative humidity is high throughout the year in Castro Valley.

The city experiences its highest humidity in January, reaching 80%. In June, the humidity drops to its lowest level at 71%. What does this mean? Read our detailed page on humidity levels for further details.

Relative humidity over the year