Helena, Montana has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 32.2 °F (low) to 56.9 °F (high). Annual precipitation averages 13.4 Inches. Helena is located in USDA Plant Hardiness Zone 5a. The growing season typically runs from the last frost around May 11 - May 20 through the first frost around Sep. 21 - Sep. 30.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 14.8 °F | 33.5 °F | 0.56 in. |
| February | 16.9 °F | 37.2 °F | 0.61 in. |
| March | 23.2 °F | 46.3 °F | 0.67 in. |
| April | 30.6 °F | 55.1 °F | 1.24 in. |
| May | 39.0 °F | 64.7 °F | 2.09 in. |
| June | 46.1 °F | 73.1 °F | 2.28 in. |
| July | 51.8 °F | 84.2 °F | 1.28 in. |
| August | 49.9 °F | 83.6 °F | 1.09 in. |
| September | 42.2 °F | 72.1 °F | 1.19 in. |
| October | 32.8 °F | 56.9 °F | 1.0 in. |
| November | 23.6 °F | 42.7 °F | 0.78 in. |
| December | 15.6 °F | 33.7 °F | 0.57 in. |
| Annual | 32.2 °F | 56.9 °F | 13.36 in. |
| Average First Frost Date | Sep. 21 - Sep. 30 |
| Average Last Frost Date | May 11 - May 20 |
| Average Days With Frost | 150-180 Days |
| Plant Hardiness Zone | Zone 5a : -20°F to -15°F |
| Plant Hardiness Zone - 2012 | Zone 4b : -25°F to -20°F |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |