Washington weather by month
Washington runs from about 3°C in January to 26°C in July, with August the wettest month at 198 mm.
warmest month
July
26°C
coolest month
January
3°C
wettest month
August
198 mm
worst air month
February
19 µg/m³
The whole year, month by month.
| Month | Avg temp | Rain | Sun | PM2.5 |
|---|---|---|---|---|
| January | 3°C | 122 mm | 168 h | 12 |
| February | 5°C | 58 mm | 231 h | 19 |
| March | 9°C | 161 mm | 249 h | 10 |
| April | 14°C | 91 mm | 260 h | 9 |
| May | 19°C | 137 mm | 283 h | 9 |
| June | 25°C | 76 mm | 379 h | 11 |
| July | 26°C | 131 mm | 351 h | 15 |
| August | 24°C | 198 mm | 334 h | 16 |
| September | 20°C | 119 mm | 241 h | 14 |
| October | 15°C | 9 mm | 296 h | 9 |
| November | 11°C | 73 mm | 228 h | 10 |
| December | 4°C | 83 mm | 198 h | 11 |
About 3,218 hours of sun a year. Roughly 126 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.