Boulder climate — normals and trends
Boulder (United States) has a warm-summer humid continental climate (Dfb) under the Köppen-Geiger classification. Its mean annual temperature is 6.3 °C and it receives 712 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 (18.9 °C on average) and the coldest is January (-5.0 °C). Rainfall peaks in May.
Boulder averages 180 frost days, 7 hot days (≥ 30 °C) and 132 rainy days per year.
Boulder has warmed by +2.5 °C between 1940 and 2025, or +0.29 °C per decade. This trend is statistically significant.
The number of frost days there went from about 190 to 170 per year over the period.
The hottest day of the period reached 35.3 °C (on 23 June 1954) and the coldest -38.7 °C (on 12 January 1963).
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
BoulderColorado
- coords
- 40.01°, -105.27°
- period
- 1940–2025 · 86 yrs
Mean daily temperature
6.3°C
Average daily high
13.4°C
Average daily low
-0.2°C
Annual rainfall
712mm
Sunshine / day
10.8h
Mean relative humidity
62%
Average peak wind
13.5km/h
Seasonal range
23.9°C
Frost days (< 0 °C)
180 d/yr
Hot days (≥ 30 °C)
7 d/yr
Rainy days (≥ 1 mm)
132 d/yr
Annual snowfall
169.3 cm
Average feels-like high
11.1 °C
Average feels-like low
-3.9 °C
Average peak gust
33.4 km/h
Tropical nights (≥ 20 °C)
0 d/yr
Solar radiation
18.5 MJ/m²
Has the climate changed?
One stripe per year, 1940 to 2025
+2.5 °C
since 1940
+0.3 °C per decade · r² = 0.48 · 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
35.3 °C
23 June 1954
Coldest day
-38.7 °C
12 January 1963
Wettest day
67 mm
8 June 1974
Windiest day
54.4 km/h
2 April 1982
Strongest gust
122.4 km/h
2 April 1982
Hottest feels-like
34.7 °C
18 July 2022
Coldest feels-like
-44.5 °C
12 January 1963
Snowiest day
36.3 cm
3 April 1986
Sunniest day
14.3 h
26 June 1946
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 | 0.1 °C | -1.7 °C | 36 mm | +10 mm |
| Feb | 3.7 °C | +0.4 °C | 38 mm | +9 mm |
| Mar | 11.6 °C | +4.6 °C | 39 mm | -17 mm |
| Apr | 13.4 °C | +1.9 °C | 64 mm | -17 mm |
| May | 17.6 °C | +1.0 °C | 140 mm | +28 mm |
| Jun | 24.2 °C | +1.3 °C | 112 mm | +27 mm |
| Jul | 27.4 °C | +1.3 °C | 66 mm | -14 mm |
| Aug | 26.1 °C | +1.0 °C | 128 mm | +50 mm |
| Sep | 21.7 °C | +0.4 °C | 81 mm | +24 mm |
| Oct | 16.4 °C | +1.5 °C | 33 mm | -14 mm |
| Nov | 12.6 °C | +5.4 °C | 7 mm | -28 mm |
| Dec | 9.9 °C | +7.1 °C | 25 mm | -2 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 Boulder?
Boulder has a warm-summer humid continental climate (Köppen Dfb). Over 1940-2025, the average annual temperature is 6.3 °C and it receives 712 mm of precipitation per year.
What is the hottest day ever recorded in Boulder?
The hottest day measured in Boulder between 1940 and 2025 was 23 June 1954, reaching 35.3 °C.
What is the coldest day in Boulder?
The coldest day measured in Boulder between 1940 and 2025 was 12 January 1963, at -38.7 °C.
Does it snow in Boulder?
Yes. Boulder gets on average 169.3 cm of snow per year and has around 180 frost days.
Has the climate of Boulder warmed?
Yes: Boulder warmed by +2.5 °C between 1940 and 2025, a statistically significant trend.
What is the wettest day in Boulder?
The wettest day measured in Boulder between 1940 and 2025 was 8 June 1974, with 67 mm of rain in 24 hours.
What was the windiest day in Boulder?
The windiest day measured in Boulder between 1940 and 2025 was 2 April 1982, with winds reaching 54.4 km/h.
What is the warmest month in Boulder?
The warmest month in Boulder is July (18.9 °C on average); the coldest is January (-5.0 °C).
How much does it rain in Boulder?
Boulder receives on average 712 mm of precipitation per year, spread over about 132 rainy days.
Is it sunny in Boulder?
Boulder gets on average 10.8 hours of sunshine per day, roughly 3,942 hours per year over 1940-2025.
What is the biggest single-day snowfall in Boulder?
The heaviest 24-hour snowfall measured in Boulder between 1940 and 2025 was 3 April 1986, with 36.3 cm.
Are there tropical nights in Boulder?
Almost never: tropical nights (temperature staying above 20 °C) are virtually non-existent in Boulder.
What was the most extreme apparent temperature in Boulder?
In Boulder, between 1940 and 2025, the highest apparent temperature reached 34.7 °C on 18 July 2022, and the lowest was -44.5 °C on 12 January 1963.
Compare Boulder with another city
Pick a second city: its normals will be set against these, indicator by indicator.
Nearby cities
The climate around Boulder