WEATHER · CLIMATE NORMALS · 1991–2020
San Jose Climate — Averages by Month
What the weather in San Jose, USaverages across a standard 30-year period. Each month's figure is the 1991–2020 mean temperature and total rainfall from the ERA5 reanalysis — the long-run normal a place settles around, not a forecast for any particular day.
Month-by-month normals
| Month | Avg temperature | Avg rainfall |
|---|---|---|
| January | 9.4 °C · coldest | 132.1 mm |
| February | 10.5 °C | 136.9 mm · wettest |
| March | 11.7 °C | 102.6 mm |
| April | 12.8 °C | 49.1 mm |
| May | 14.7 °C | 24.1 mm |
| June | 16.9 °C | 4.7 mm |
| July | 18.5 °C | 1.0 mm |
| August | 18.8 °C · warmest | 1.3 mm |
| September | 18.7 °C | 2.9 mm |
| October | 16.3 °C | 30.5 mm |
| November | 12.2 °C | 62.9 mm |
| December | 9.4 °C | 121.3 mm |
How to read these numbers
These are reanalysis normals, not readings from a single weather station. They come from the ERA5 0.25° (~25 km) global reanalysis grid, sampled at the grid cell nearest San Jose — centred at 37.25°N, 122.00°W. A reanalysis blends observations with a physics model onto an even grid, so a coastal or mountain city's cell can read a little cooler, warmer, wetter or drier than the city centre itself. The month-to-month shape — when it's hot, when it rains — is what these normals capture best.
“Normal” means the 1991–2020 average, the current World Meteorological Organization standard period. A normal is what a place tends toward over decades — any single day, month or year can and will depart from it.