Weatheo

Boulder Weather by Month

Average temperatures, rainfall and humidity for Boulder, United States, month by month, built from OpenWeather’s historical records. Use it to see what a typical Boulder month looks like before you travel — then check the live Boulder forecast for the days ahead.

Warmest month

July

31°C average high

Coolest month

January

-5°C average low

Wettest month

May

99 mm of rain

Driest month

December

7 mm of rain

Average temperature and rainfall in Boulder by month

Averages of the daily highs and lows recorded in each month, with total rainfall, mean humidity and mean wind speed.

MonthAvg highAvg lowRecord low / highRainfallHumidityWind
January7°C-5°C-23°C / 20°C
8 mm
57%11 km/h
February8°C-5°C-23°C / 25°C
8 mm
56%13 km/h
March14°C0°C-22°C / 31°C
24 mm
51%13 km/h
April17°C3°C-14°C / 29°C
36 mm
49%14 km/h
May21°C7°C-10°C / 32°C
99 mm
57%11 km/h
June29°C13°C4°C / 38°C
48 mm
47%10 km/h
July31°C17°C8°C / 38°C
49 mm
47%10 km/h
August30°C16°C6°C / 38°C
39 mm
48%10 km/h
September27°C12°C-2°C / 36°C
37 mm
46%10 km/h
October19°C4°C-15°C / 41°C
21 mm
51%10 km/h
November13°C0°C-25°C / 27°C
9 mm
52%10 km/h
December8°C-4°C-25°C / 23°C
7 mm
54%10 km/h

Best time to visit Boulder

The most comfortable time to visit Boulder is generally June and September to October, balancing mild daytime temperatures against the driest stretch of the year. The city has strongly marked seasons and rain concentrates around May, totalling about 385 mm a year.

Travellers who prefer heat should aim for July, when highs average 31°C. May is the month to avoid if rain would spoil your plans — it averages 99 mm, roughly 14× the rainfall of the driest month (December).

Source: OpenWeather historical and statistical weather data. Values are long-term averages, not a forecast — see the Boulder forecast for what is happening now.

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