Castro Valley weather by month
What a typical year looks like in Castro Valley, California: average highs and lows, rain and snow, and the warmest and coldest days on record. Normals are the 1991–2020 averages at OAKLAND INTERNATIONAL AIRPORT, 15 km from Castro Valley; records cover 1948–2026.
The year at a glance
- Precipitation a year
- 18.7 in474 mm
- Snow a year
- Rare
- Last spring freeze
- Jan 18
- First fall freeze
- Dec 5
- Heating degree days
- 2,691
- Cooling degree days
- 176
Freeze dates are medians (half of years earlier, half later). Degree days use a 65°F base; HVAC design temperatures here are 33°1° (heating, 99%) and 91°33° (cooling, 1%).
Month by month
Castro Valley in January
Highs average 58°14° and lows 42°6°, with 3.4 in87 mm of precipitation in a typical January.
- Record high
- 83°28° (2021)
- Record low
- 25°−4° (1949)
- Heating degree days
- 470
- Cooling degree days
- 0
Castro Valley in February
Highs average 60°16° and lows 45°7°, with 3.5 in89 mm of precipitation in a typical February.
- Record high
- 84°29° (2021)
- Record low
- 28°−2° (1949)
- Heating degree days
- 351
- Cooling degree days
- 0
Castro Valley in March
Highs average 63°17° and lows 47°8°, with 2.7 in69 mm of precipitation in a typical March.
- Record high
- 86°30° (2004)
- Record low
- 32°0° (1953)
- Heating degree days
- 309
- Cooling degree days
- 1
Castro Valley in April
Highs average 66°19° and lows 49°10°, with 1.4 in34 mm of precipitation in a typical April.
- Record high
- 91°33° (2009)
- Record low
- 35°2° (1955)
- Heating degree days
- 234
- Cooling degree days
- 4
Castro Valley in May
Highs average 68°20° and lows 52°11°, with 0.63 in16 mm of precipitation in a typical May.
- Record high
- 98°37° (1975)
- Record low
- 39°4° (1950)
- Heating degree days
- 170
- Cooling degree days
- 12
Castro Valley in June
Highs average 71°22° and lows 54°12°, with 0.18 in4.6 mm of precipitation in a typical June.
- Record high
- 100°38° (2000)
- Record low
- 43°6° (1950)
- Heating degree days
- 92
- Cooling degree days
- 24
Castro Valley in July
Highs average 72°22° and lows 56°13°, with 0 in0 mm of precipitation in a typical July.
- Record high
- 99°37° (1959)
- Record low
- 48°9° (1955)
- Heating degree days
- 59
- Cooling degree days
- 25
Castro Valley in August
Highs average 72°22° and lows 57°14°, with 0.04 in1 mm of precipitation in a typical August.
- Record high
- 99°37° (2010)
- Record low
- 48°9° (1952)
- Heating degree days
- 50
- Cooling degree days
- 39
Castro Valley in September
Highs average 74°23° and lows 56°13°, with 0.1 in2.5 mm of precipitation in a typical September.
- Record high
- 104°40° (2020)
- Record low
- 41°5° (1950)
- Heating degree days
- 56
- Cooling degree days
- 50
Castro Valley in OctoberThis month
Highs average 72°22° and lows 51°11°, with 0.88 in22 mm of precipitation in a typical October.
- Record high
- 100°38° (2024)
- Record low
- 36°2° (1949)
- Heating degree days
- 133
- Cooling degree days
- 20
Castro Valley in November
Highs average 64°18° and lows 46°8°, with 2 in51 mm of precipitation in a typical November.
- Record high
- 85°29° (2008)
- Record low
- 31°−1° (2004)
- Heating degree days
- 305
- Cooling degree days
- 1
Castro Valley in December
Highs average 58°14° and lows 42°6°, with 3.8 in98 mm of precipitation in a typical December.
- Record high
- 79°26° (2020)
- Record low
- 26°−3° (1972)
- Heating degree days
- 462
- Cooling degree days
- 0