Helsinki weather by month
Helsinki runs from about -7°C in January to 18°C in July, with September the wettest month at 113 mm.
warmest month
July
18°C
coolest month
January
-7°C
wettest month
September
113 mm
worst air month
March
8 µg/m³
The whole year, month by month.
| Month | Avg temp | Rain | Sun | PM2.5 |
|---|---|---|---|---|
| January | -7°C | 44 mm | 49 h | 6 |
| February | -3°C | 85 mm | 95 h | 7 |
| March | 0°C | 39 mm | 159 h | 8 |
| April | 3°C | 85 mm | 186 h | 4 |
| May | 12°C | 4 mm | 463 h | 4 |
| June | 17°C | 39 mm | 468 h | 5 |
| July | 18°C | 86 mm | 392 h | 6 |
| August | 18°C | 69 mm | 392 h | 4 |
| September | 15°C | 113 mm | 283 h | 5 |
| October | 9°C | 65 mm | 174 h | 4 |
| November | 4°C | 97 mm | 77 h | 5 |
| December | 1°C | 78 mm | 40 h | 5 |
About 2,778 hours of sun a year. Roughly 82 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.