Basel weather by month
Basel runs from about 3°C in January to 22°C in August, with September the wettest month at 145 mm.
warmest month
August
22°C
coolest month
January
3°C
wettest month
September
145 mm
worst air month
December
18 µg/m³
The whole year, month by month.
| Month | Avg temp | Rain | Sun | PM2.5 |
|---|---|---|---|---|
| January | 3°C | 99 mm | 135 h | 15 |
| February | 7°C | 75 mm | 138 h | 10 |
| March | 9°C | 93 mm | 219 h | 16 |
| April | 10°C | 108 mm | 251 h | 12 |
| May | 14°C | 141 mm | 288 h | 8 |
| June | 18°C | 138 mm | 301 h | 7 |
| July | 20°C | 100 mm | 371 h | 5 |
| August | 22°C | 58 mm | 365 h | 9 |
| September | 15°C | 145 mm | 232 h | 7 |
| October | 13°C | 93 mm | 183 h | 10 |
| November | 6°C | 105 mm | 166 h | 13 |
| December | 3°C | 91 mm | 128 h | 18 |
About 2,777 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 2026-05-24. Full method, licences and the list of sources we rejected are on the methodology page.