Koyasan weather by month
Koyasan runs from about 1°C in January to 24°C in August, with June the wettest month at 331 mm.
warmest month
August
24°C
coolest month
January
1°C
wettest month
June
331 mm
worst air month
February
19 µg/m³
The whole year, month by month.
| Month | Avg temp | Rain | Sun | PM2.5 |
|---|---|---|---|---|
| January | 1°C | 74 mm | 203 h | 13 |
| February | 3°C | 151 mm | 170 h | 19 |
| March | 4°C | 253 mm | 234 h | 18 |
| April | 12°C | 162 mm | 199 h | 18 |
| May | 14°C | 320 mm | 254 h | 13 |
| June | 18°C | 331 mm | 248 h | 15 |
| July | 24°C | 155 mm | 318 h | 14 |
| August | 24°C | 173 mm | 328 h | 16 |
| September | 22°C | 125 mm | 291 h | 13 |
| October | 16°C | 207 mm | 212 h | 12 |
| November | 9°C | 168 mm | 222 h | 18 |
| December | 1°C | 38 mm | 244 h | 15 |
About 2,923 hours of sun a year. Roughly 211 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 2026-05-25. Full method, licences and the list of sources we rejected are on the methodology page.