Boulder, Colorado has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 2.8 °C (low) to 18.4 °C (high). Annual precipitation averages 480.1 Millimeters. Boulder is located in USDA Plant Hardiness Zone 6a. The growing season typically runs from the last frost around May 1 - May 10 through the first frost around Oct. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -6.9 °C | 7.7 °C | 15.24 mm |
| February | -6.2 °C | 8.2 °C | 20.07 mm |
| March | -2.1 °C | 13.2 °C | 44.45 mm |
| April | 1.3 °C | 16.4 °C | 66.8 mm |
| May | 6.3 °C | 21.2 °C | 77.72 mm |
| June | 11.3 °C | 28 °C | 46.23 mm |
| July | 14.7 °C | 31.4 °C | 45.72 mm |
| August | 13.6 °C | 30.3 °C | 36.07 mm |
| September | 9.2 °C | 25.9 °C | 50.8 mm |
| October | 2.6 °C | 18.7 °C | 37.34 mm |
| November | -2.8 °C | 12.1 °C | 23.11 mm |
| December | -6.9 °C | 7.3 °C | 16.51 mm |
| Annual | 2.8 °C | 18.4 °C | 480.06 mm |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | 125-150 Days |
| Plant Hardiness Zone | Zone 6a : -23.3°C to -20.6°C |
| Plant Hardiness Zone - 2012 | Zone 6a : -23.3°C to -20.6°C |
| Current Drought Conditions | Severe Drought |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |