Haarlem weather by month
Haarlem runs from about 5°C in January to 19°C in August, with May the wettest month at 142 mm.
warmest month
August
19°C
coolest month
January
5°C
wettest month
May
142 mm
worst air month
March
15 µg/m³
The whole year, month by month.
| Month | Avg temp | Rain | Sun | PM2.5 |
|---|---|---|---|---|
| January | 5°C | 77 mm | 119 h | 14 |
| February | 8°C | 133 mm | 104 h | 11 |
| March | 8°C | 51 mm | 188 h | 15 |
| April | 10°C | 108 mm | 280 h | 9 |
| May | 15°C | 142 mm | 354 h | 9 |
| June | 15°C | 76 mm | 341 h | 8 |
| July | 18°C | 120 mm | 345 h | 7 |
| August | 19°C | 57 mm | 360 h | 8 |
| September | 16°C | 120 mm | 274 h | 8 |
| October | 13°C | 63 mm | 208 h | 6 |
| November | 8°C | 124 mm | 107 h | 8 |
| December | 7°C | 96 mm | 55 h | 10 |
About 2,735 hours of sun a year. Roughly 117 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 2026-05-27. Full method, licences and the list of sources we rejected are on the methodology page.