Boulder climate
Boulder (Colorado, United States) has a humid subtropical climate (Köppen Cfa). The average temperature over the year is 11 °C53 °F, and about 448 mm18 in of precipitation falls in an average year.
Temperature by month
Precipitation by month
Boulder climate table
| Month | High °C°F | Low °C°F | Mean °C°F | Precip. mmin | Frost days |
|---|---|---|---|---|---|
| Jan | 643 | −523 | 133 | 190.8 | 29 |
| Feb | 745 | −522 | 133 | 241.0 | 26 |
| Mar | 1355 | −229 | 642 | 361.4 | 22 |
| Apr | 1763 | 235 | 1049 | 542.1 | 12 |
| May | 2373 | 745 | 1559 | 652.6 | 3 |
| Jun | 3087 | 1356 | 2271 | 421.7 | 0 |
| Jul | 3392 | 1763 | 2577 | 522.0 | 0 |
| Aug | 3188 | 1661 | 2474 | 431.7 | 0 |
| Sep | 2780 | 1152 | 1966 | 361.4 | 0 |
| Oct | 1966 | 338 | 1152 | 331.3 | 7 |
| Nov | 1253 | −229 | 541 | 210.8 | 20 |
| Dec | 642 | −522 | 032 | 210.8 | 28 |
| Year | 3392 | −522 | 1153 | 44818 | 148 |
“Year” row: highest monthly high, lowest monthly low, annual mean and annual total. Frost days are for the whole grid cell.
| Month | Humid. | Cloud | Solar | Daylight |
|---|---|---|---|---|
| Jan | 55% | 61% | 2.5 | 9:37 |
| Feb | 56% | 64% | 3.5 | 10:38 |
| Mar | 51% | 65% | 4.7 | 11:50 |
| Apr | 49% | 67% | 5.4 | 13:13 |
| May | 49% | 67% | 6.0 | 14:22 |
| Jun | 41% | 51% | 7.0 | 14:00 |
| Jul | 42% | 52% | 6.6 | 14:45 |
| Aug | 43% | 55% | 5.8 | 13:44 |
| Sep | 42% | 46% | 5.0 | 12:24 |
| Oct | 47% | 52% | 3.7 | 11:04 |
| Nov | 51% | 56% | 2.6 | 9:54 |
| Dec | 57% | 62% | 2.1 | 9:20 |
Humid. = average relative humidity at 2 m; cloud = average cloud amount; solar = average daily solar energy reaching the ground in kWh/m² (all-sky); daylight in hours:minutes, calculated for the 15th of each month.
What the climate of Boulder is like
The warmest month is July, with an average high of 33 °C92 °F and a low of 17 °C63 °F. The coldest is December, when highs average 6 °C42 °F and lows −5 °C22 °F. Seasons are strongly marked: the warmest month is on average 25.1 °C45.3 °F warmer than the coldest.
Annual precipitation is moderate at about 448 mm18 in. The wettest three-month stretch is April–June, which brings 36% of the annual total. Months with less than 20 mm0.8 in on average: January. The wettest month is May (65 mm2.6 in), the driest is January (19 mm0.8 in).
Relative humidity ranges from 41% in June to 57% in December. The clearest skies (lowest average cloud amount, 46%) are typical of September. Average wind speed near the ground ranges from 7 km/h (5 mph) in September to 10 km/h (7 mph) in January. Daylight lasts from about 9.3 hours in December to 15.0 hours in June.
A lasting snow cover is typical in November–March, when the average snow depth in the reanalysis exceeds 10 cm (deepest in January, about 16 cm).
Best time to visit Boulder
Based on these averages, the most comfortable months for sightseeing and outdoor activities are May and September: average highs of 23 °C73 °F to 27 °C80 °F with 36 mm1.4 in to 65 mm2.6 in of precipitation per month.
The most challenging month is December, which is cold, with average highs of 6 °C42 °F.
Comfort score: months are ranked by how close they come to an average high of 21–28 °C (70–82 °F), lows above 5 °C (41 °F), little precipitation and moderate humidity. The best-ranked months of each place are recommended, even where none meets all of these. These are general rules of thumb applied to long-term averages.
What to pack for Boulder
- Winter (December–February) — highs 642 to 7 °C45 °F, lows around −5 °C22 °F, about 22 mm0.9 in of precipitation a month. Pack a warm coat, layers and closed shoes, an extra layer for the cooler mornings and evenings and shoes with good grip, as frost is common.
- Spring (March–May) — highs 1355 to 23 °C73 °F, lows −229 to 7 °C45 °F, about 52 mm2.0 in of precipitation a month. Pack long sleeves, a sweater and a medium jacket and an extra layer for the cooler mornings and evenings.
- Summer (June–August) — highs 3087 to 33 °C92 °F, lows 1356 to 17 °C63 °F, about 46 mm1.8 in of precipitation a month. Pack very light, breathable clothing, a sun hat and plenty of water and an extra layer for the cooler mornings and evenings.
- Autumn (September–November) — highs 1253 to 27 °C80 °F, lows −229 to 11 °C52 °F, about 30 mm1.2 in of precipitation a month. Pack light layers — T-shirts plus a light sweater or jacket and an extra layer for the cooler mornings and evenings.
How Boulder compares
Compared with Westminster, about 28 km to the southeast, Boulder has practically the same average temperature and receives a similar amount of precipitation.
Of the 222 places in the United States covered by World Climates, Boulder is the 162nd warmest by annual mean temperature and the 179th wettest by annual precipitation. See all of them on the United States climate page.
Places in other countries with the most similar temperature and rainfall pattern: Pyatigorsk (Russia, Dfa), Sunzha (Ordzhonikidzevskaya) (Russia, Dfa) and Simferopol (Ukraine, Cfa).
Nearby places
- Westminster 28 km · 11 °C52 °F · 448 mm18 in
- Thornton 30 km · 11 °C53 °F · 448 mm18 in
- Lakewood 38 km · 12 °C53 °F · 440 mm17 in
- Denver 39 km · 12 °C54 °F · 440 mm17 in
- Fort Collins 65 km · 12 °C53 °F · 450 mm18 in
- Greeley 66 km · 12 °C54 °F · 450 mm18 in
- Colorado Springs 137 km · 11 °C52 °F · 402 mm16 in
- Pueblo 204 km · 13 °C56 °F · 353 mm14 in
Frequently asked questions
What is the warmest month in Boulder?
July is the warmest month in Boulder, with an average high of 33 °C (92 °F) and an average low of 17 °C (63 °F).
What is the coldest month in Boulder?
December is the coldest month, with an average high of 6 °C (42 °F) and an average low of -5 °C (22 °F).
When does it rain the most in Boulder?
May is the wettest month with about 65 mm (2.6 in) of precipitation; January is the driest with about 19 mm (0.8 in).
What is the best time to visit Boulder?
Judging by long-term averages, the most comfortable months are May and September.
About this data
All figures are 25-year averages (January 2001 – December 2025) from the NASA POWER project. Temperature, humidity, wind and precipitation come from the MERRA-2 reanalysis (precipitation is the bias-corrected MERRA-2 product), cloud and solar values from CERES satellite data. They describe a grid cell of roughly 50–70 km, not a single weather station, so they can differ from airport records — most of all on coasts, in mountains and for rainfall. Average highs and lows are the monthly mean temperature plus/minus half of the average daily temperature range. Counts of rainy days are not part of this dataset.
The grid cell’s average elevation is 1,801 m, while Boulder lies at about 1,624 m. Temperatures on this page were therefore adjusted by +1.2 °C2.1 °F using the standard lapse rate of 6.5 °C per 1,000 m.