Boulder, Montana has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 28.4 °F (low) to 56 °F (high). Annual precipitation averages 11.5 Inches. Boulder is located in USDA Plant Hardiness Zone 4b. The growing season typically runs from the last frost around Jun. 1 - Jun. 10 through the first frost around Sep.1 - Sep. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 11.8 °F | 34.3 °F | 0.3 in. |
| February | 14.4 °F | 37.3 °F | 0.26 in. |
| March | 20.8 °F | 45.7 °F | 0.5 in. |
| April | 27.0 °F | 53.5 °F | 0.85 in. |
| May | 35.1 °F | 62.8 °F | 1.95 in. |
| June | 42.2 °F | 71.0 °F | 2.35 in. |
| July | 47.6 °F | 82.3 °F | 1.53 in. |
| August | 45.6 °F | 81.6 °F | 1.05 in. |
| September | 37.9 °F | 70.8 °F | 0.93 in. |
| October | 28.3 °F | 56.6 °F | 0.75 in. |
| November | 18.8 °F | 42.2 °F | 0.62 in. |
| December | 11.6 °F | 33.3 °F | 0.41 in. |
| Annual | 28.4 °F | 56 °F | 11.5 in. |
| Average First Frost Date | Sep.1 - Sep. 10 |
| Average Last Frost Date | Jun. 1 - Jun. 10 |
| Average Days With Frost | Over 180 Days |
| Plant Hardiness Zone | Zone 4b : -25°F to -20°F |
| Plant Hardiness Zone - 2012 | Zone 4a : -30°F to -25°F |
| Current Drought Conditions | Moderate Drought |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |