Boston weather by month
Boston runs from about -1°C in January to 25°C in July, with March the wettest month at 209 mm.
warmest month
July
25°C
coolest month
January
-1°C
wettest month
March
209 mm
worst air month
February
15 µg/m³
The whole year, month by month.
| Month | Avg temp | Rain | Sun | PM2.5 |
|---|---|---|---|---|
| January | -1°C | 193 mm | 164 h | 10 |
| February | 1°C | 35 mm | 242 h | 15 |
| March | 5°C | 209 mm | 215 h | 10 |
| April | 8°C | 93 mm | 245 h | 10 |
| May | 15°C | 135 mm | 307 h | 10 |
| June | 21°C | 80 mm | 361 h | 11 |
| July | 25°C | 89 mm | 356 h | 12 |
| August | 22°C | 77 mm | 354 h | 14 |
| September | 18°C | 57 mm | 285 h | 10 |
| October | 12°C | 27 mm | 283 h | 7 |
| November | 8°C | 72 mm | 224 h | 8 |
| December | 1°C | 137 mm | 194 h | 8 |
About 3,230 hours of sun a year. Roughly 122 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.