Boulder (CO) Temperature by Month

Boulder, Colorado, United States of America has an average annual maximum temperature of 18°C (64°F), ranging from 7°C (45°F) in December to 31°C (88°F) in July. Below you'll find a full monthly breakdown and a comparison with cities worldwide.

The climate in Boulder is known for significant temperature differences throughout the year. At night, this contrast is just as clear, with lows ranging from 15°C (59°F) in July to -7°C (19°F) in December.

The chart below illustrates the average maximum day and minimum night temperatures in Boulder by month:

The minimum temperature is often recorded between 4 AM and 6 AM, while the highest temperature is usually reached at 3 PM, when the sun's heating effect is strongest. July, the warmest month, gets 323 hours of sunshine.

The chart below shows the average temperature throughout the year:

Boulder's average annual maximum temperature is 18°C (64°F). To put that in context, here's how it compares to a few well-known destinations:

Seville, Spain averages 23°C (73°F) a year, one of the warmer cities in Western Europe, with long hot summers.

Toronto, Canada averages 13°C (55°F) annually, with cold snowy winters balanced by genuinely warm summers.

Chicago, USA averages 15°C (59°F) annually, known for extreme seasonal swings, from bitterly cold winters to warm summers.

Melbourne, Australia averages 20°C (68°F) annually, known for unpredictable weather, with four seasons sometimes happening in one day.

Temperature alone doesn't tell the whole story, humidity plays a big role in how warm or cold it actually feels. High humidity in summer makes the heat feel more intense, particularly once temperatures climb above 25°C. In winter, the same humidity can make cold air feel sharper than the thermometer suggests.

In the cooler months, when temperatures drop below 10°C, high humidity makes the cold feel more cutting than it would in dry conditions.

In Boulder, December is the coolest month, with average highs of 7°C (45°F) and humidity around 56%, considered moderate. In July, the warmest month, temperatures average 31°C (88°F) with 46% humidity, conditions that feel moderate. For a full picture, see our humidity page.

Climate temperature data is typically calculated as a 30-year average. This smooths out year-to-year variability and gives a more reliable picture of what a place is actually like, rather than what happened in any single unusual year.

The readings come from a range of sources, land-based weather stations, ocean buoys, ships, and satellites. That data is collected by weather services around the world, then pooled, quality-checked, and averaged to produce the climate records you see here.

Seasonal temperature shifts influence more than just how warm it feels, they also drive changes in rainfall, cloud cover, and wind patterns throughout the year.

Warmer air holds more moisture, which tends to mean heavier or more frequent rain during the warmer months. When temperatures drop in winter, any precipitation that does fall is more likely to come as snow or sleet, though in Boulder this rarely lasts long on the ground.

For more on Boulder's weather, including monthly rainfall, sunshine hours, and humidity, visit our Boulder climate page.