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Dedham, Massachusetts climate

Cfa Humid subtropical

Dedham has a strongly seasonal cool-temperate climate (Humid subtropical, Köppen Cfa). The hottest month is July with an average daily high near 29°C, while the coldest is January averaging around −7°C at night. Precipitation is fairly even year-round, totalling about 1254 mm.

☀️ Summers

Warm

Highs near 29°C in July.

About 18 days a year above 32 °C

❄️ Winters

Very cold

Lows near −7°C in January.

About 109 freezing nights a year

🌧️ Rain

Wet

About 1254 mm of rain a year.

Wettest in December

⛅ Sky & trend

Partly cloudy

A roughly even mix of sun and cloud.

+0.4 °C vs 50 years ago

Temperature & precipitation

Daily high–low temperature range with the monthly average, plus monthly precipitation · 1991–2020 normals · hover a month for the exact figures

Clear vs cloudy days

Share of days each month that are clear, partly cloudy or cloudy · 1991–2020 · hover a month for the day counts

Dedham climate normals (1991–2020)

	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Avg high (°C)	3	4	8	15	21	26	29	28	24	18	11	6
Avg temp (°C)	−2	−1	3	9	15	20	24	23	18	12	6	1
Avg low (°C)	−7	−6	−2	3	9	14	18	17	13	6	1	−4
Precipitation (mm)	98	91	114	110	92	106	89	94	101	128	101	129

Jan – Jun	Jan	Feb	Mar	Apr	May	Jun
Avg high (°C)	3	4	8	15	21	26
Avg temp (°C)	−2	−1	3	9	15	20
Avg low (°C)	−7	−6	−2	3	9	14
Precipitation (mm)	98	91	114	110	92	106

Jul – Dec	Jul	Aug	Sep	Oct	Nov	Dec
Avg high (°C)	29	28	24	18	11	6
Avg temp (°C)	24	23	18	12	6	1
Avg low (°C)	18	17	13	6	1	−4
Precipitation (mm)	89	94	101	128	101	129

How often — frequency of weather events

	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Days with measurable rain (days)	10	8	10	10	11	10	9	8	9	10	9	10
Days with high ≥ 32°C (days)	—	—	—	0.2	1	3	7	5	1	—	—	—
Days with low ≤ 0°C (days)	25	22	18	6	0.2	—	—	—	0.0	3	13	23
Days with snowfall ≥ 2.5 cm (days)	3	2	2	0.4	—	—	—	—	—	0.1	0.2	2

Jan – Jun	Jan	Feb	Mar	Apr	May	Jun
Days with measurable rain (days)	10	8	10	10	11	10
Days with high ≥ 32°C (days)	—	—	—	0.2	1	3
Days with low ≤ 0°C (days)	25	22	18	6	0.2	—
Days with snowfall ≥ 2.5 cm (days)	3	2	2	0.4	—	—

Jul – Dec	Jul	Aug	Sep	Oct	Nov	Dec
Days with measurable rain (days)	9	8	9	10	9	10
Days with high ≥ 32°C (days)	7	5	1	—	—	—
Days with low ≤ 0°C (days)	—	—	0.0	3	13	23
Days with snowfall ≥ 2.5 cm (days)	—	—	—	0.1	0.2	2

Sky & atmosphere

	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Cloud cover (%)	63	62	62	64	65	63	57	56	55	60	62	63
Clear days (≤ 30% cloud)	5	5	6	5	5	5	6	7	9	7	6	5
Partly cloudy days (30–70%)	11	11	10	10	10	11	14	12	10	10	10	12
Cloudy days (≥ 70%)	14	13	14	15	16	14	11	12	11	14	14	14
Relative humidity (%)	88	87	83	80	79	79	74	73	74	78	82	86
Wind speed (km/h)	3.7	4.2	3.7	2.3	1.6	1.4	1.3	1.4	1.7	2.2	2.4	2.8

Jan – Jun	Jan	Feb	Mar	Apr	May	Jun
Cloud cover (%)	63	62	62	64	65	63
Clear days (≤ 30% cloud)	5	5	6	5	5	5
Partly cloudy days (30–70%)	11	11	10	10	10	11
Cloudy days (≥ 70%)	14	13	14	15	16	14
Relative humidity (%)	88	87	83	80	79	79
Wind speed (km/h)	3.7	4.2	3.7	2.3	1.6	1.4

Jul – Dec	Jul	Aug	Sep	Oct	Nov	Dec
Cloud cover (%)	57	56	55	60	62	63
Clear days (≤ 30% cloud)	6	7	9	7	6	5
Partly cloudy days (30–70%)	14	12	10	10	10	12
Cloudy days (≥ 70%)	11	12	11	14	14	14
Relative humidity (%)	74	73	74	78	82	86
Wind speed (km/h)	1.3	1.4	1.7	2.2	2.4	2.8

Methodology & sources

Temperature & precipitation — the official 1991–2020 climate normals from NOAA's U.S. Climate Normals, measured at Jamaica Plain (NOAA GHCN station USC00193890), about 8 km from the city centre.

Cloud, humidity, wind & sunshine — modelled estimates from NASA POWER, NASA's satellite-and-reanalysis climatology. This is the standard global source for atmospheric variables, which are not measured at most weather stations.

How we build these numbers →