National Weather Service Forecast for: Castro Valley CA
Issued by: National Weather Service San Francisco Bay Area/Monterey, CA
Updated: 1:40 am PST Dec 18, 2025
 
Overnight

Overnight: Patchy fog. Otherwise, mostly cloudy, with a low around 47. Calm wind.
Patchy Fog

 Thursday

Thursday: Patchy fog before 11am. Otherwise, cloudy, then gradually becoming mostly sunny, with a high near 61. Light and variable wind.
Patchy Fog
then Mostly
Sunny
 Thursday
Night
Thursday Night: A 20 percent chance of rain after 10pm. Mostly cloudy, with a low around 50. Calm wind.
Slight Chance
Rain
 Friday

Friday: Rain, mainly after 10am. High near 62. South wind 6 to 9 mph. Chance of precipitation is 80%. New precipitation amounts of less than a tenth of an inch possible.
Rain

 Friday
Night
Friday Night: Rain, mainly before 10pm. Low around 54. South wind 5 to 7 mph. Chance of precipitation is 90%. New precipitation amounts of less than a tenth of an inch possible.
Rain then
Chance Rain
 Saturday

Saturday: Rain, mainly after 10am. High near 60. Chance of precipitation is 80%. New precipitation amounts of less than a tenth of an inch possible.
Rain

 Saturday
Night
Saturday Night: Rain. Low around 55. Chance of precipitation is 90%.
Rain

 Sunday

Sunday: Rain. Cloudy, with a high near 62.
Rain

 Sunday
Night
Sunday Night: Rain. Cloudy, with a low around 54.
Rain
Lo 47 °F Hi 61 °F Lo 50 °F Hi 62 °F Lo 54 °F Hi 60 °F Lo 55 °F Hi 62 °F Lo 54 °F

 

Overnight
 
 Patchy fog. Otherwise, mostly cloudy, with a low around 47. Calm wind.
Thursday
 
 Patchy fog before 11am. Otherwise, cloudy, then gradually becoming mostly sunny, with a high near 61. Light and variable wind.
Thursday Night
 
 A 20 percent chance of rain after 10pm. Mostly cloudy, with a low around 50. Calm wind.
Friday
 
 Rain, mainly after 10am. High near 62. South wind 6 to 9 mph. Chance of precipitation is 80%. New precipitation amounts of less than a tenth of an inch possible.
Friday Night
 
 Rain, mainly before 10pm. Low around 54. South wind 5 to 7 mph. Chance of precipitation is 90%. New precipitation amounts of less than a tenth of an inch possible.
Saturday
 
 Rain, mainly after 10am. High near 60. Chance of precipitation is 80%. New precipitation amounts of less than a tenth of an inch possible.
Saturday Night
 
 Rain. Low around 55. Chance of precipitation is 90%.
Sunday
 
 Rain. Cloudy, with a high near 62.
Sunday Night
 
 Rain. Cloudy, with a low around 54.
Monday
 
 Rain. Cloudy, with a high near 59.
Monday Night
 
 Rain likely. Cloudy, with a low around 49.
Tuesday
 
 Rain likely. Cloudy, with a high near 58.
Tuesday Night
 
 Rain. Mostly cloudy, with a low around 49.
Wednesday
 
 Rain likely. Mostly cloudy, with a high near 58.

 

Forecast from NOAA-NWS for Castro Valley CA.