Castro Valley (CA) Weather & Climate: Best Time to Visit
Average temperatures, rainfall, sunshine and the best time to visit Castro Valley.
Climate overview of Castro Valley
Castro Valley, California, United States of America, has a moderate seasonal temperature range, with September reaching 25°C (77°F) and December cooling to 14°C (57°F).
Castro Valley sees a moderate amount of rainfall, totalling around 512 mm (20 in) per year. It experiences a distinct dry season from May to October, with warm summers and mild winters, creating some seasonal variation. Sunshine peaks in May, when the city sees around 10.8 hours of sunshine per day.
Castro Valley Weather by Month
Pick a month to see the average temperature, rainfall and sunshine in Castro Valley - and find the best time to visit.
Monthly Temperature in Castro Valley
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
Rainfall in Castro Valley
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
Sunshine Hours in Castro Valley
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
Humidity in Castro Valley by Month
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
Best Time to Visit Castro Valley
Monthly ratings reflect general weather comfort, based on daytime temperature and rainfall. Swimming and winter conditions are highlighted separately where relevant.
- Best overall: May, June, July, August, September and October
- Warmest weather: June, July, August and September
- Most sunshine: April, May, June and July
- Fewest rainy days: June, July, August and September
- Wettest months: January, February, March, April, November and December, when rainfall is highest.
- Seasonal pattern: A distinct dry season from May to October, with warm summers and mild winters
Frequently asked questions about the climate in Castro Valley
What is the best time to visit Castro Valley?
May, June, July, August, September and October typically offer the most optimal weather in Castro Valley. In contrast, December tends to have less optimal conditions. Castro Valley has a distinct dry season from May to October, with warm summers and mild winters.
What temperatures can I expect in Castro Valley?
Daytime highs range from 14°C (57°F) in December to 25°C (77°F) in September. Nighttime lows range from 5°C (41°F) to 13°C (55°F).
How much rain does Castro Valley get?
Annual rainfall is around 512 mm (20 in). December is the wettest month with 111 mm (4.4 in), while August is the driest with 0.1 mm (0 in).
How sunny is Castro Valley?
Castro Valley receives around 3,058 hours of sunshine per year. May is the sunniest month with 324 hours, while December is the cloudiest with just 160 hours. Overall, Castro Valley enjoys abundant sunshine.
Castro Valley 3-Day Forecast
Castro Valley (CA) 3-Day Forecast
Castro Valley on the map
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