Boulder, CO Climate & Monthly Averages
The climate of Boulder
Located in Colorado, United States, Boulder experiences a humid subtropical climate with hot, humid summers and generally mild winters. Afternoon temperatures peak near 85°F (30°C) in July and dip to about 38°F (3°C) in January, with around 20.6 inches (524 mm) of precipitation falling across the year.
Climate quick facts
- Hottest month: July - highs near 85°F (30°C)
- Coldest month: January - highs near 38°F (3°C)
- Record high: 98°F (37°C) · Record low: -24°F (-31°C) (2015–2024)
- Wettest month: May (15 rainy days) · Sunniest: July (13.1 h sun/day)
- Climate type: humid subtropical - hot, humid summers and generally mild winters
- Snow: about 34 days a year
Temperatures through the year
The warmest stretch of the year centers on July. Highs average 85°F (30°C) and overnight lows stay near 59°F (15°C). The coolest month is January, with typical highs of 38°F (3°C) and lows around 17°F (-8°C). Based on 2015–2024 weather data, temperatures have reached as high as 98°F (37°C) and dropped as low as -24°F (-31°C).
Rain, sun and snow
May is usually the wettest month. It brings about 4.6 inches (116 mm) of rain over 15 days, while December is the driest. July brings the most sunshine, averaging 13.1 hours of sun a day. Snow falls on about 34 days in a typical year, mostly from October through May.
Monthly climate table
| Month | High | Low | Rain days | Precipitation | Sunshine | Humidity |
|---|---|---|---|---|---|---|
| January | 38° | 17° | 6 | 1.0 in | 7.9 h/day | 61% |
| February | 39° | 15° | 7 | 1.4 in | 9.1 h/day | 61% |
| March | 49° | 24° | 8 | 2.1 in | 10.1 h/day | 61% |
| April | 57° | 31° | 10 | 2.3 in | 10.9 h/day | 58% |
| May | 65° | 41° | 15 | 4.6 in | 11.7 h/day | 64% |
| June | 80° | 54° | 8 | 1.9 in | 13.0 h/day | 52% |
| July | 85° | 59° | 9 | 1.5 in | 13.1 h/day | 50% |
| August | 83° | 58° | 8 | 1.4 in | 12.3 h/day | 50% |
| September | 78° | 52° | 6 | 1.0 in | 11.2 h/day | 47% |
| October | 63° | 38° | 6 | 1.3 in | 9.7 h/day | 53% |
| November | 49° | 27° | 6 | 1.3 in | 8.5 h/day | 57% |
| December | 42° | 20° | 5 | 0.9 in | 7.8 h/day | 56% |
Boulder month by month
Boulder weather in January
January brings highs around 38°F (3°C), lows near 17°F (-8°C), about 6 wet days and roughly 5 snowy days - typically the coldest month of the year in Boulder.
Boulder weather in February
February brings highs around 39°F (4°C), lows near 15°F (-9°C), about 7 wet days and roughly 6 snowy days.
Boulder weather in March
March brings highs around 49°F (9°C), lows near 24°F (-5°C), about 8 wet days and roughly 5 snowy days.
Boulder weather in April
April brings highs around 57°F (14°C), lows near 31°F (0°C), about 10 wet days and roughly 5 snowy days.
Boulder weather in May
May brings highs around 65°F (18°C), lows near 41°F (5°C), about 15 wet days and roughly 2 snowy days - typically the wettest month of the year in Boulder.
Boulder weather in June
June brings highs around 80°F (26°C), lows near 54°F (12°C), about 8 wet days.
Boulder weather in July
July brings highs around 85°F (30°C), lows near 59°F (15°C), about 9 wet days - typically the hottest month and the sunniest month of the year in Boulder.
Boulder weather in August
August brings highs around 83°F (28°C), lows near 58°F (14°C), about 8 wet days.
Boulder weather in September
September brings highs around 78°F (26°C), lows near 52°F (11°C), about 6 wet days.
Boulder weather in October
October brings highs around 63°F (17°C), lows near 38°F (3°C), about 6 wet days and roughly 2 snowy days.
Boulder weather in November
November brings highs around 49°F (10°C), lows near 27°F (-3°C), about 6 wet days and roughly 4 snowy days.
Boulder weather in December
December brings highs around 42°F (5°C), lows near 20°F (-6°C), about 5 wet days and roughly 4 snowy days - typically the driest month of the year in Boulder.
Seasons in Boulder
Spring (March through May)
Spring in Boulder is mild, with daytime highs averaging 57°F (14°C) and nights around 32°F (0°C); expect showers on roughly 33 days across the season, plus around 13 snowy days.
Summer (June through August)
Summer in Boulder is hot, with daytime highs averaging 83°F (28°C) and nights around 57°F (14°C); expect showers on roughly 25 days across the season.
Fall (September through November)
Fall in Boulder stays on the cool side of mild, with daytime highs averaging 64°F (18°C) and nights around 39°F (4°C); expect showers on roughly 18 days across the season, plus around 7 snowy days.
Winter (December through February)
Winter in Boulder runs cold, with daytime highs averaging 40°F (4°C) and nights around 18°F (-8°C); expect showers on roughly 18 days across the season, plus around 14 snowy days.
Climate questions, answered
What is the average temperature in Boulder?
Is Boulder hot in summer?
Is Boulder cold in winter?
How many rainy days does Boulder get in a year?
Best time to visit Boulder
The best time to visit Boulder is generally August to October and June, when warm days, manageable rainfall and plenty of daylight line up. Daytime temperatures in that window typically sit near 76°F (24°C).
Pack for Boulder with a heavy insulated coat, hat and gloves for winter; a compact umbrella or rain shell - showers are a regular feature. Evenings can feel noticeably cooler than afternoons - July nights average 59°F (15°C).
Boulder temperature records (2015-2024)
Derived from ERA5 reanalysis data, 2015–2024. Official station records may differ.