Boulder, CO Climate & Monthly Averages
The climate of 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.
Climate quick facts
- 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%
Temperatures through the year
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.
Rain, sun and snow
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.
How Boulder compares
- 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.
Ranked against every city in our dataset, each measured on the same ten-year window.
Monthly climate table
| 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% |
Boulder month by month
Average high and low for each month, with the bar showing where it sits in Boulder's year (left is the coldest night, right is the 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
Warmer places to go, by month: January · February · March · April · May · June · July · August · September · October · November · December
Seasons 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.
Climate questions, answered
How much sun does Boulder get?
Is Boulder humid?
How cold does Boulder get in winter?
How hot does Boulder get in summer?
How much do temperatures drop at night in Boulder?
Does it freeze in Boulder?
Best time to visit Boulder
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.
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.
Boulder temperature records (2015-2024)
Derived from ERA5 reanalysis data, 2015–2024. Official station records may differ. Need the precipitation in other units? The mm-to-inches rainfall converter handles it.