Castro Valley Climate by Month
Castro Valley, California, United States
Warm summers and mild winters, with most rain from December to March.
The climate in Castro Valley is one of warm summers and mild winters, with most rain from December to March. Afternoon highs range from 59°F (15°C) in January to 81°F (27°C) in September, and December nights average 43°F (6°C). It gets 17 in (441 mm) of rain a year, 71% of it from December to March. June to September are almost completely dry.
- Warmest month
- 81°F(27°C)
- Average high, September
- Coldest nights
- 43°F(6°C)
- Average low, December
- Rain per year
- 17 in(441 mm)
- Wettest: January
- Humidity
- 65%
- Sunniest: June
Best and worst months in Castro Valley
Best for weatherMay, June and October are the best time for weather in Castro Valley: highs near 76°F (24°C) and almost no rain.
Least pleasantJanuary is the least pleasant month: it's the coldest, with highs of only 59°F (15°C).
Comfort combines how close the afternoon high is to 75°F (24°C) with how much rain falls and how humid it is. See where the weather is best in June.
Temperature and rain through the year
Highs and lows (°F)
Average highAverage low
Rain (in per month)
Castro Valley weather by month
| Month | High | Low | Rain | Humidity | Sun |
|---|---|---|---|---|---|
| JanJanuary | 59°F(15°C) | 43°F(6°C) | 3.5 in(89 mm) | 78% | 1.9 |
| FebFebruary | 63°F(17°C) | 45°F(7°C) | 3.3 in(83 mm) | 70% | 2.6 |
| MarMarch | 66°F(19°C) | 47°F(8°C) | 2.5 in(63 mm) | 64% | 4.2 |
| AprApril | 70°F(21°C) | 48°F(9°C) | 1.3 in(33 mm) | 65% | 5.5 |
| MayMayBest | 73°F(23°C) | 51°F(11°C) | 0.6 in(14 mm) | 63% | 6.3 |
| JunJuneBest | 78°F(25°C) | 55°F(13°C) | 0.2 in(4 mm) | 59% | 7.3 |
| JulJuly | 79°F(26°C) | 56°F(14°C) | 0.0 in(1 mm) | 60% | 7.2 |
| AugAugust | 80°F(27°C) | 57°F(14°C) | 0.0 in(1 mm) | 63% | 6.5 |
| SepSeptember | 81°F(27°C) | 56°F(13°C) | 0.1 in(2 mm) | 59% | 5.4 |
| OctOctoberBest | 76°F(25°C) | 52°F(11°C) | 1.0 in(26 mm) | 59% | 3.8 |
| NovNovember | 67°F(19°C) | 47°F(8°C) | 1.9 in(47 mm) | 70% | 2.5 |
| DecDecember | 60°F(16°C) | 43°F(6°C) | 3.1 in(78 mm) | 70% | 1.8 |
1991–2020 averages. Sun is solar radiation in kWh/m² per day. Highlighted: the most comfortable months.
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