WEATHER · CLIMATE NORMALS · 1991–2020
Seattle Climate — Averages by Month
What the weather in Seattle, 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 | 5.5 °C | 182.3 mm |
| February | 6.1 °C | 127.4 mm |
| March | 7.8 °C | 146.1 mm |
| April | 10.0 °C | 120.6 mm |
| May | 13.3 °C | 82.2 mm |
| June | 15.8 °C | 66.0 mm |
| July | 18.7 °C | 29.4 mm |
| August | 18.8 °C · warmest | 36.0 mm |
| September | 16.0 °C | 70.6 mm |
| October | 11.5 °C | 139.2 mm |
| November | 7.6 °C | 198.5 mm · wettest |
| December | 5.2 °C · coldest | 184.4 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 Seattle — centred at 47.50°N, 122.25°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.