Siena weather by month
Siena runs from about 5°C in December to 27°C in July, with October the wettest month at 186 mm.
warmest month
July
27°C
coolest month
December
5°C
wettest month
October
186 mm
worst air month
December
17 µg/m³
The whole year, month by month.
| Month | Avg temp | Rain | Sun | PM2.5 |
|---|---|---|---|---|
| January | 7°C | 57 mm | 199 h | 11 |
| February | 9°C | 114 mm | 186 h | 11 |
| March | 11°C | 112 mm | 240 h | 13 |
| April | 13°C | 74 mm | 343 h | 9 |
| May | 16°C | 125 mm | 363 h | 6 |
| June | 21°C | 30 mm | 394 h | 6 |
| July | 27°C | 5 mm | 438 h | 6 |
| August | 27°C | 33 mm | 386 h | 8 |
| September | 19°C | 159 mm | 292 h | 5 |
| October | 16°C | 186 mm | 217 h | 5 |
| November | 10°C | 19 mm | 239 h | 9 |
| December | 5°C | 56 mm | 207 h | 17 |
About 3,504 hours of sun a year. Roughly 98 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.