Boulder, Montana has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from -2 °C (low) to 13.3 °C (high). Annual precipitation averages 292.1 Millimeters. 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 | -11.2 °C | 1.3 °C | 7.62 mm |
| February | -9.8 °C | 2.9 °C | 6.6 mm |
| March | -6.2 °C | 7.6 °C | 12.7 mm |
| April | -2.8 °C | 11.9 °C | 21.59 mm |
| May | 1.7 °C | 17.1 °C | 49.53 mm |
| June | 5.7 °C | 21.7 °C | 59.69 mm |
| July | 8.7 °C | 27.9 °C | 38.86 mm |
| August | 7.6 °C | 27.6 °C | 26.67 mm |
| September | 3.3 °C | 21.6 °C | 23.62 mm |
| October | -2.1 °C | 13.7 °C | 19.05 mm |
| November | -7.3 °C | 5.7 °C | 15.75 mm |
| December | -11.3 °C | 0.7 °C | 10.41 mm |
| Annual | -2 °C | 13.3 °C | 292.09 mm |
| 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 : -31.7°C to -28.9°C |
| Plant Hardiness Zone - 2012 | Zone 4a : -34.4°C to -31.7°C |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |