National Weather Service Forecast for: Castro Valley CA
Issued by: National Weather Service San Francisco Bay Area/Monterey, CA
Updated: 8:05 pm PST Dec 5, 2025
 
Tonight

Tonight: Mostly clear, with a low around 44. Calm wind.
Mostly Clear

 Saturday

Saturday: Sunny, with a high near 64. Calm wind becoming west around 6 mph in the afternoon.
Sunny

 Saturday
Night
Saturday Night: Mostly clear, with a low around 45. Light east wind.
Mostly Clear

 Sunday

Sunday: Mostly sunny, with a high near 64. Calm wind becoming west northwest around 5 mph in the afternoon.
Mostly Sunny

 Sunday
Night
Sunday Night: Partly cloudy, with a low around 46. Calm wind.
Partly Cloudy

 Monday

Monday: Patchy fog before 9am. Otherwise, mostly sunny, with a high near 65.
Patchy Fog
then Mostly
Sunny
 Monday
Night
Monday Night: Partly cloudy, with a low around 47.
Partly Cloudy

 Tuesday

Tuesday: Mostly sunny, with a high near 66.
Mostly Sunny

 Tuesday
Night
Tuesday Night: Partly cloudy, with a low around 48.
Partly Cloudy
Lo 44 °F Hi 64 °F Lo 45 °F Hi 64 °F Lo 46 °F Hi 65 °F Lo 47 °F Hi 66 °F Lo 48 °F

Coastal Flood Advisory
 

Tonight
 
 Mostly clear, with a low around 44. Calm wind.
Saturday
 
 Sunny, with a high near 64. Calm wind becoming west around 6 mph in the afternoon.
Saturday Night
 
 Mostly clear, with a low around 45. Light east wind.
Sunday
 
 Mostly sunny, with a high near 64. Calm wind becoming west northwest around 5 mph in the afternoon.
Sunday Night
 
 Partly cloudy, with a low around 46. Calm wind.
Monday
 
 Patchy fog before 9am. Otherwise, mostly sunny, with a high near 65.
Monday Night
 
 Partly cloudy, with a low around 47.
Tuesday
 
 Mostly sunny, with a high near 66.
Tuesday Night
 
 Partly cloudy, with a low around 48.
Wednesday
 
 Mostly sunny, with a high near 67.
Wednesday Night
 
 Patchy fog. Otherwise, mostly clear, with a low around 48.
Thursday
 
 Patchy fog. Otherwise, mostly sunny, with a high near 67.
Thursday Night
 
 Mostly clear, with a low around 48.
Friday
 
 Mostly sunny, with a high near 67.

 

Forecast from NOAA-NWS for Castro Valley CA.