Portsmouth climate — normals and trends
Portsmouth (United States) has a warm-summer humid continental climate (Dfb) under the Köppen-Geiger classification. Its mean annual temperature is 9.1 °C and it receives 1,132 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 (20.8 °C on average) and the coldest is January (-2.9 °C). Rainfall peaks in December.
Portsmouth averages 95 frost days, 1 hot days (≥ 30 °C) and 122 rainy days per year.
Portsmouth has warmed by +1.6 °C between 1940 and 2025, or +0.18 °C per decade. This trend is statistically significant.
The number of frost days there went from about 104 to 86 per year over the period.
The hottest day of the period reached 32.7 °C (on 2 August 1975) and the coldest -23.6 °C (on 4 February 2023).
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
PortsmouthNew Hampshire
- coords
- 43.08°, -70.76°
- period
- 1940–2025 · 86 yrs
Mean daily temperature
9.1°C
Average daily high
12.2°C
Average daily low
6.0°C
Annual rainfall
1,132mm
Sunshine / day
8.8h
Mean relative humidity
73%
Average peak wind
22.3km/h
Seasonal range
23.7°C
Frost days (< 0 °C)
95 d/yr
Hot days (≥ 30 °C)
1 d/yr
Rainy days (≥ 1 mm)
122 d/yr
Annual snowfall
114.4 cm
Average feels-like high
10.0 °C
Average feels-like low
2.5 °C
Average peak gust
40.4 km/h
Tropical nights (≥ 20 °C)
12 d/yr
Solar radiation
14.3 MJ/m²
Has the climate changed?
One stripe per year, 1940 to 2025
+1.6 °C
since 1940
+0.2 °C per decade · r² = 0.38 · 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
32.7 °C
2 August 1975
Coldest day
-23.6 °C
4 February 2023
Wettest day
112 mm
11 September 1954
Windiest day
68.4 km/h
31 August 1954
Strongest gust
136.1 km/h
26 February 2010
Hottest feels-like
39.4 °C
2 August 1975
Coldest feels-like
-33.4 °C
4 February 2023
Snowiest day
33.0 cm
18 February 1952
Sunniest day
14.9 h
16 June 1940
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 | 0.2 °C | -0.3 °C | 47 mm | -48 mm |
| Feb | 0.9 °C | -0.5 °C | 98 mm | +9 mm |
| Mar | 7.5 °C | +2.6 °C | 112 mm | +6 mm |
| Apr | 11.8 °C | +1.6 °C | 128 mm | +25 mm |
| May | 15.4 °C | -0.1 °C | 176 mm | +84 mm |
| Jun | 21.7 °C | +1.1 °C | 52 mm | -34 mm |
| Jul | 25.6 °C | +1.7 °C | 72 mm | -9 mm |
| Aug | 23.5 °C | +0.1 °C | 30 mm | -54 mm |
| Sep | 21.1 °C | +1.3 °C | 60 mm | -23 mm |
| Oct | 15.7 °C | +1.2 °C | 110 mm | +12 mm |
| Nov | 8.5 °C | -0.4 °C | 66 mm | -42 mm |
| Dec | 1.6 °C | -1.6 °C | 94 mm | -15 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 Portsmouth?
Portsmouth has a warm-summer humid continental climate (Köppen Dfb). Over 1940-2025, the average annual temperature is 9.1 °C and it receives 1,132 mm of precipitation per year.
What is the hottest day ever recorded in Portsmouth?
The hottest day measured in Portsmouth between 1940 and 2025 was 2 August 1975, reaching 32.7 °C.
What is the coldest day in Portsmouth?
The coldest day measured in Portsmouth between 1940 and 2025 was 4 February 2023, at -23.6 °C.
Does it snow in Portsmouth?
Yes. Portsmouth gets on average 114.4 cm of snow per year and has around 95 frost days.
Has the climate of Portsmouth warmed?
Yes: Portsmouth warmed by +1.6 °C between 1940 and 2025, a statistically significant trend.
What is the wettest day in Portsmouth?
The wettest day measured in Portsmouth between 1940 and 2025 was 11 September 1954, with 112 mm of rain in 24 hours.
What was the windiest day in Portsmouth?
The windiest day measured in Portsmouth between 1940 and 2025 was 31 August 1954, with winds reaching 68.4 km/h.
What is the warmest month in Portsmouth?
The warmest month in Portsmouth is July (20.8 °C on average); the coldest is January (-2.9 °C).
How much does it rain in Portsmouth?
Portsmouth receives on average 1,132 mm of precipitation per year, spread over about 122 rainy days.
Is it sunny in Portsmouth?
Portsmouth gets on average 8.8 hours of sunshine per day, roughly 3,212 hours per year over 1940-2025.
What is the biggest single-day snowfall in Portsmouth?
The heaviest 24-hour snowfall measured in Portsmouth between 1940 and 2025 was 18 February 1952, with 33.0 cm.
Are there tropical nights in Portsmouth?
Yes: Portsmouth has on average 12 tropical nights per year (temperature staying above 20 °C), over 1940-2025.
What was the most extreme apparent temperature in Portsmouth?
In Portsmouth, between 1940 and 2025, the highest apparent temperature reached 39.4 °C on 2 August 1975, and the lowest was -33.4 °C on 4 February 2023.
Compare Portsmouth with another city
Pick a second city: its normals will be set against these, indicator by indicator.
Nearby cities
The climate around Portsmouth