Boston weather in December
In December, Boston has daytime highs averaging 4.8 °C, nights around -2.5 °C, with 10 wet days, and a sea temperature of 7.5 °C. Figures are 1991–2020 climate normals.
- 4.8°C Average high
- -2.5°C Average low
- 10days Wet days
- 116mm Rainfall
- 7.5°C Sea temperature
- 9.1h Daylight
Daily temperatures through December
How December develops
Averages for the first, middle and last part of the month, from daily 1991–2020 normals. Chance of rain is the share of years in which that calendar day recorded more than 1 mm.
| Days | Avg high | Avg low | Chance of rain |
|---|---|---|---|
| 1–10 December | 6.2 °C | -0.9 °C | 31 % |
| 11–20 December | 4.5 °C | -2.7 °C | 35 % |
| 21–31 December | 3.9 °C | -3.6 °C | 33 % |
- Average highs fall from 6.2 °C early in December to 3.9 °C by the end of it.
What to expect
| Measure | Typical December | Share of the month |
|---|---|---|
| Days above 25 °C | 0 of 31 | 0 % |
| Days above 30 °C | 0 of 31 | 0 % |
| Days below 0 °C | 22 of 31 | 69 % |
| Days with more than 1 mm rain | 10 of 31 | 33 % |
Conditions in December
| Measure | Average |
|---|---|
| Mean temperature | 0.7 °C |
| Record high (1991–2020) | 20 °C |
| Record low (1991–2020) | -19 °C |
| Relative humidity | 72 % |
| Wind speed | 23 km/h |
| Cloud cover | 58 % |
Where Boston ranks in December
| Ranking | Position | Value |
|---|---|---|
| The coolest places in North America in December | 48thof 50 | 4.8 °C |
December compared with the months around it
| Month | Avg high | Rainfall | Cloud |
|---|---|---|---|
| January | 1.9 °C | 93 mm | 57 % |
| February | 3.3 °C | 83 mm | 57 % |
| October | 16.3 °C | 108 mm | 53 % |
| November | 10.2 °C | 94 mm | 56 % |
| December | 4.8 °C | 116 mm | 58 % |
See all twelve months for Boston
- December is the 10th warmest month here.
- It is the 11th driest month of the year.
- It ranks 8th for least cloud cover.
- Days last about 9.1 hours from sunrise to sunset.
- It rains on 10 of 31 days — 33 % of the month.
- Nights are about 7.3 °C cooler than the middle of the day.
- The hottest December day on record since 1991 reached 20 °C, 15 °C above the usual daytime high.
QuestionsDecember in Boston, answered
How warm is Boston in December?
Daily highs average 4.8 °C and nights fall to about -2.5 °C, a spread of 7.3 °C between afternoon and dawn. That makes December the 10th warmest month of the year here.
Does it rain much in Boston in December?
December averages 116 mm of rain, spread over about 10 of the 31 days — 33 % of the month. Cloud cover averages 58 % of the sky.
Is the sea warm enough to swim in December?
The sea averages 7.5 °C off Boston in December. Most people find water below 20 °C bracing and above 25 °C comfortable for a long swim; this figure is a monthly surface average, so a sheltered bay on a still afternoon can be warmer.
How long are the days in December?
Boston averages 9.1 hours between sunrise and sunset in December. Day length is computed from latitude and date, so it is exact rather than modelled — but it says nothing about how much of that time is sunny.
Data sources and method
- ERA5 / ERA5-Land reanalysis — Copernicus Climate Change Service (C3S), ECMWF. Copernicus Licence
- Open-Meteo — Open-Meteo.com. CC BY 4.0
- NOAA OISST v2.1 — NOAA Physical Sciences Laboratory. Public domain
- GeoNames — GeoNames.org. CC BY 4.0
- Normal period
- 1991–2020
- Dataset version
- era5-1991-2020-scores1.1
- Last processed
Measured values come from ERA5 reanalysis and are reproduced unchanged. Calculated by us: daylight hours, beach and comfort scores, monthly rankings, threshold day counts, chance of a wet day by date, ten-day averages within the month. Full formulas are on the methodology page.
Contains modified Copernicus Climate Change Service information 2026. Neither the European Commission nor ECMWF is responsible for any use that may be made of the Copernicus information or data it contains.