Seattle weather by month
Seattle runs from about 5°C in January to 20°C in July, with January the wettest month at 226 mm.
warmest month
July
20°C
coolest month
January
5°C
wettest month
January
226 mm
worst air month
September
15 µg/m³
The whole year, month by month.
| Month | Avg temp | Rain | Sun | PM2.5 |
|---|---|---|---|---|
| January | 5°C | 226 mm | 92 h | 13 |
| February | 6°C | 108 mm | 116 h | 10 |
| March | 7°C | 89 mm | 242 h | 8 |
| April | 9°C | 42 mm | 253 h | 9 |
| May | 12°C | 56 mm | 294 h | 11 |
| June | 15°C | 57 mm | 346 h | 9 |
| July | 20°C | 17 mm | 416 h | 8 |
| August | 19°C | 48 mm | 314 h | 12 |
| September | 16°C | 39 mm | 258 h | 15 |
| October | 12°C | 118 mm | 206 h | 8 |
| November | 8°C | 156 mm | 122 h | 9 |
| December | 7°C | 206 mm | 120 h | 8 |
About 2,779 hours of sun a year. Roughly 119 rainy days a year.
These are long-run climate normals, not a forecast. A given year can sit well outside them. PM2.5 is a global model: near the coast it counts sea salt as fine particulate and reads high against ground stations, sometimes by a factor of two. Use the shape of the year, not the absolute number.
where these numbers come from
- · Temperature, rainfall and sunshine: ECMWF ERA5 reanalysis climate normals via Open-Meteo (CC BY 4.0), fetched once and stored.
- · PM2.5: Copernicus CAMS reanalysis, monthly means. Modelled, not station readings; near coasts CAMS counts sea salt as PM2.5 and reads high.
Last reviewed 2026-05-23. Full method, licences and the list of sources we rejected are on the methodology page.