Acton climate — normals and trends
Acton (United States) has a hot-summer humid continental climate (Dfa) under the Köppen-Geiger classification. Its mean annual temperature is 9.8 °C and it receives 1,056 mm of precipitation per year.
These figures are normals computed over 86 complete calendar years, from 1940 to 2025, using ERA5 reanalysis data from the Copernicus programme.
The warmest month is July (22.6 °C on average) and the coldest is January (-3.2 °C). Rainfall peaks in March.
Acton averages 115 frost days, 24 hot days (≥ 30 °C) and 118 rainy days per year.
Acton has warmed by +1.7 °C between 1940 and 2025, or +0.20 °C per decade. This trend is statistically significant.
The number of frost days there went from about 124 to 106 per year over the period.
The hottest day of the period reached 39.5 °C (on 2 August 1975) and the coldest -29.2 °C (on 13 February 1967).
Data from ERA5 reanalysis (Copernicus Climate Change Service), redistributed under a CC-BY 4.0 licence. Normals are recomputed whenever the archive is updated.
Climate normals · ERA5
ActonMassachusetts
- coords
- 42.49°, -71.43°
- period
- 1940–2025 · 86 yrs
Mean daily temperature
9.8°C
Average daily high
14.7°C
Average daily low
5.1°C
Annual rainfall
1,056mm
Sunshine / day
8.6h
Mean relative humidity
68%
Average peak wind
16.5km/h
Seasonal range
25.8°C
Frost days (< 0 °C)
115 d/yr
Hot days (≥ 30 °C)
24 d/yr
Rainy days (≥ 1 mm)
118 d/yr
Annual snowfall
119.7 cm
Average feels-like high
12.7 °C
Average feels-like low
2.2 °C
Average peak gust
38.9 km/h
Tropical nights (≥ 20 °C)
17 d/yr
Solar radiation
14.1 MJ/m²
Has the climate changed?
One stripe per year, 1940 to 2025
+1.7 °C
since 1940
+0.2 °C per decade · r² = 0.43 · p = < 0.001
Trend fitted by linear regression (ordinary least squares) on annual means. A trend is shown only when it is statistically significant (p < 0.05).
A climograph overlays rainfall (bars) and temperature (line): the standard reading in climatology, where you can see at a glance whether the warm season is also the dry one.
Records for the period
Hottest day
39.5 °C
2 August 1975
Coldest day
-29.2 °C
13 February 1967
Wettest day
146 mm
19 August 1955
Windiest day
53.3 km/h
19 August 1991
Strongest gust
128.5 km/h
26 November 1950
Hottest feels-like
43.7 °C
2 August 1975
Coldest feels-like
-34.5 °C
13 February 1967
Snowiest day
39.5 cm
12 December 1992
Sunniest day
14.8 h
10 June 1941
Normals computed over complete calendar years 1940–2025.
A specific year
Pick a year and see how it compares to normal — warmer, drier or more extreme than usual?
Across the whole year
Month by month
| High | vs. normal | Precipitation | vs. normal | |
|---|---|---|---|---|
| Jan | 0.8 °C | -0.3 °C | 49 mm | -36 mm |
| Feb | 2.0 °C | -0.5 °C | 84 mm | +2 mm |
| Mar | 10.6 °C | +3.4 °C | 88 mm | -10 mm |
| Apr | 15.6 °C | +1.8 °C | 94 mm | +1 mm |
| May | 19.6 °C | -0.2 °C | 217 mm | +129 mm |
| Jun | 25.7 °C | +0.8 °C | 52 mm | -33 mm |
| Jul | 29.7 °C | +1.7 °C | 72 mm | -9 mm |
| Aug | 27.1 °C | +0.2 °C | 40 mm | -46 mm |
| Sep | 23.8 °C | +1.2 °C | 67 mm | -13 mm |
| Oct | 17.1 °C | +0.7 °C | 108 mm | +22 mm |
| Nov | 9.4 °C | -0.5 °C | 68 mm | -26 mm |
| Dec | 2.0 °C | -1.6 °C | 84 mm | -13 mm |
The year's extremes
What was the weather like that day?
Your birthday, a wedding, a memorable trip: discover the actual weather for any date since 1940.
Frequently asked questions
What is the climate of Acton?
Acton has a hot-summer humid continental climate (Köppen Dfa). Over 1940-2025, the average annual temperature is 9.8 °C and it receives 1,056 mm of precipitation per year.
What is the hottest day ever recorded in Acton?
The hottest day measured in Acton between 1940 and 2025 was 2 August 1975, reaching 39.5 °C.
What is the coldest day in Acton?
The coldest day measured in Acton between 1940 and 2025 was 13 February 1967, at -29.2 °C.
Does it snow in Acton?
Yes. Acton gets on average 119.7 cm of snow per year and has around 115 frost days.
Has the climate of Acton warmed?
Yes: Acton warmed by +1.7 °C between 1940 and 2025, a statistically significant trend.
What is the wettest day in Acton?
The wettest day measured in Acton between 1940 and 2025 was 19 August 1955, with 146 mm of rain in 24 hours.
What was the windiest day in Acton?
The windiest day measured in Acton between 1940 and 2025 was 19 August 1991, with winds reaching 53.3 km/h.
What is the warmest month in Acton?
The warmest month in Acton is July (22.6 °C on average); the coldest is January (-3.2 °C).
How much does it rain in Acton?
Acton receives on average 1,056 mm of precipitation per year, spread over about 118 rainy days.
Is it sunny in Acton?
Acton gets on average 8.6 hours of sunshine per day, roughly 3,139 hours per year over 1940-2025.
What is the biggest single-day snowfall in Acton?
The heaviest 24-hour snowfall measured in Acton between 1940 and 2025 was 12 December 1992, with 39.5 cm.
Are there tropical nights in Acton?
Yes: Acton has on average 17 tropical nights per year (temperature staying above 20 °C), over 1940-2025.
What was the most extreme apparent temperature in Acton?
In Acton, between 1940 and 2025, the highest apparent temperature reached 43.7 °C on 2 August 1975, and the lowest was -34.5 °C on 13 February 1967.
Compare Acton with another city
Pick a second city: its normals will be set against these, indicator by indicator.
Nearby cities
The climate around Acton