Boulder, CO Climate & Monthly Averages
Boulder has a humid subtropical climate. July is the hottest month, averaging 85° by day; January is the coldest at 38°.
Winter sets the pace in Boulder
Seasons are the whole story in Boulder. The gap between an average July and an average January is 25°C - hot, humid summers and generally mild winters - which in practice means 85°F (30°C) afternoons at one end of the calendar and 38°F (3°C) at the other.
July
85° by day 59° at nightJanuary
38° by day 17° at nightThe cold-weather pattern in numbers
January sits at the other end of the year: 38°F (3°C) by day, 17°F (-8°C) at night. Warmth peaks in July: highs of 85°F (30°C), lows of 59°F (15°C). Across the gridded 2015-2024 daily record, the highest daily maximum for this location was 98°F (37°C) and the lowest daily minimum -24°F (-31°C). May is the wettest month at 4.6 inches (116 mm) over 15 days; December is the driest.
Between the average July and the average January lie 25°C, a wider spread than roughly 84% of the cities we track. Snow falls on roughly 34 days a year, mostly October through May.
More climate facts for Boulder
- Hottest month: July - highs near 85°F (30°C)
- Coldest month: January - highs near 38°F (3°C)
- Decade extremes (2015-2024): 98°F (37°C) high · -24°F (-31°C) low
- Wettest month: May (15 rainy days) · Sunniest: July (13.1 h sun/day)
- Climate type: humid subtropical
- Annual swing: 25°C between the average warmest and coolest month · day to night: 14°C
- Snow: about 34 days a year
- Months with freezing average lows: 6
- Average humidity: 56%
From snow season to the warmest stretch in Boulder
Spring (March through May)
Spring runs cool rather than cold here - highs near 57°F (14°C), nights near 32°F (0°C), and rain falls on around 33 of the 90 days, plus about 13 snowy days. Daylight is generous - around 10.9 hours of sun a day.
Summer (June through August)
Summer brings hot afternoons here - highs near 83°F (28°C), nights near 57°F (14°C), and expect showers on roughly 25 days across the season. Daylight is generous - around 12.8 hours of sun a day.
Fall (September through November)
Fall is crisp but comfortable here - highs near 64°F (18°C), nights near 39°F (4°C), and expect showers on roughly 18 days across the season, plus about 7 snowy days.
Winter (December through February)
Winter in Boulder is brisk and 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 about 14 snowy days.
The coldest and warmest values in the dataset
Derived from ERA5 reanalysis data, 2015–2024. Official station records may differ. Need another precipitation unit? Use the rainfall converter.
Planning around winter in Boulder
The easier weather window
The best time to visit Boulder is generally August to October and June, when these are the warmest and brightest weeks of the year. Daytime temperatures in that window sit near 76°F (24°C), with rain on about 7 days a month. For the same question asked the other way round, see where else is warm in August.
Cold-weather packing
Pack for Boulder with light clothing for the warm months, a heavy insulated coat, hat and gloves for winter and a compact umbrella or rain shell. July nights average 59°F (15°C), so evenings rarely match the afternoons.
Monthly highs, lows and seasonal change
| Month | High | Low | Rain days | Precipitation | Sunshine | Daylight | Wet-day chance | Humidity |
|---|---|---|---|---|---|---|---|---|
| January | 38° | 17° | 6 | 1.0 in | 7.9 h/day | 9.6 h | 18% | 61% |
| February | 39° | 15° | 7 | 1.4 in | 9.1 h/day | 10.6 h | 26% | 61% |
| March | 49° | 24° | 8 | 2.1 in | 10.1 h/day | 11.8 h | 27% | 61% |
| April | 57° | 31° | 10 | 2.3 in | 10.9 h/day | 13.2 h | 32% | 58% |
| May | 65° | 41° | 15 | 4.6 in | 11.7 h/day | 14.4 h | 47% | 64% |
| June | 80° | 54° | 8 | 1.9 in | 13.0 h/day | 15.0 h | 28% | 52% |
| July | 85° | 59° | 9 | 1.5 in | 13.1 h/day | 14.7 h | 29% | 50% |
| August | 83° | 58° | 8 | 1.4 in | 12.3 h/day | 13.7 h | 25% | 50% |
| September | 78° | 52° | 6 | 1.0 in | 11.2 h/day | 12.4 h | 21% | 47% |
| October | 63° | 38° | 6 | 1.3 in | 9.7 h/day | 11.1 h | 20% | 53% |
| November | 49° | 27° | 6 | 1.3 in | 8.5 h/day | 9.9 h | 20% | 57% |
| December | 42° | 20° | 5 | 0.9 in | 7.8 h/day | 9.3 h | 17% | 56% |
The route from winter to summer, month by month
Each card shows the average high and low. The bar places that month between Boulder's coldest night and warmest afternoon.
January
- Rain
- 6 days
- Sunshine
- 7.9 h
- Daylight
- 9.6 h
- Snow
- 5 days
February
- Rain
- 7 days
- Sunshine
- 9.1 h
- Daylight
- 10.6 h
- Snow
- 6 days
March
- Rain
- 8 days
- Sunshine
- 10.1 h
- Daylight
- 11.8 h
- Snow
- 5 days
April
- Rain
- 10 days
- Sunshine
- 10.9 h
- Daylight
- 13.2 h
- Snow
- 5 days
May
- Rain
- 15 days
- Sunshine
- 11.7 h
- Daylight
- 14.4 h
- Snow
- 2 days
June
- Rain
- 8 days
- Sunshine
- 13.0 h
- Daylight
- 15.0 h
July
- Rain
- 9 days
- Sunshine
- 13.1 h
- Daylight
- 14.7 h
August
- Rain
- 8 days
- Sunshine
- 12.3 h
- Daylight
- 13.7 h
September
- Rain
- 6 days
- Sunshine
- 11.2 h
- Daylight
- 12.4 h
October
- Rain
- 6 days
- Sunshine
- 9.7 h
- Daylight
- 11.1 h
- Snow
- 2 days
November
- Rain
- 6 days
- Sunshine
- 8.5 h
- Daylight
- 9.9 h
- Snow
- 4 days
December
- Rain
- 5 days
- Sunshine
- 7.8 h
- Daylight
- 9.3 h
- Snow
- 4 days
Looking for warmer alternatives? Browse warm places by month, or compare Boulder's coolest part of the year: January, February, December.
Where Boulder sits among other climates
- Afternoons run 14°C above the following night - a bigger day-to-night gap than 97% of the 3496 cities we track.
- Boulder averages 48°F (9°C) across the year - cooler than all but 6% of the 3496 cities we track.
- Relative humidity averages 56% - drier than all but 10% of the 3496 cities we track.
These comparisons use the same ten-year window for every city in the dataset.