WEATHER · CLIMATE NORMALS · 1991–2020
Boston Climate — Averages by Month
What the weather in Boston, USaverages across a standard 30-year period. Each month's figure is the 1991–2020 mean temperature and total rainfall from the ERA5 reanalysis — the long-run normal a place settles around, not a forecast for any particular day.
Month-by-month normals
| Month | Avg temperature | Avg rainfall |
|---|---|---|
| January | -1.1 °C · coldest | 97.8 mm |
| February | -0.3 °C | 86.4 mm |
| March | 3.0 °C | 119.2 mm |
| April | 8.5 °C | 103.5 mm |
| May | 13.8 °C | 84.7 mm |
| June | 19.0 °C | 90.6 mm |
| July | 22.4 °C · warmest | 75.5 mm |
| August | 21.7 °C | 88.8 mm |
| September | 18.0 °C | 90.7 mm |
| October | 12.2 °C | 111.1 mm |
| November | 6.8 °C | 97.2 mm |
| December | 1.9 °C | 119.5 mm · wettest |
How to read these numbers
These are reanalysis normals, not readings from a single weather station. They come from the ERA5 0.25° (~25 km) global reanalysis grid, sampled at the grid cell nearest Boston — centred at 42.25°N, 71.00°W. A reanalysis blends observations with a physics model onto an even grid, so a coastal or mountain city's cell can read a little cooler, warmer, wetter or drier than the city centre itself. The month-to-month shape — when it's hot, when it rains — is what these normals capture best.
“Normal” means the 1991–2020 average, the current World Meteorological Organization standard period. A normal is what a place tends toward over decades — any single day, month or year can and will depart from it.