East Helena, Montana has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 0.3 °C (low) to 14.2 °C (high). Annual precipitation averages 321.3 Millimeters. East Helena is located in USDA Plant Hardiness Zone 4b. 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 | -9.8 °C | 0.9 °C | 9.65 mm |
| February | -8.3 °C | 3.1 °C | 13.21 mm |
| March | -4.7 °C | 8.3 °C | 15.24 mm |
| April | -0.6 °C | 13.3 °C | 34.29 mm |
| May | 4.1 °C | 18.5 °C | 65.02 mm |
| June | 8.1 °C | 23.2 °C | 55.88 mm |
| July | 11.2 °C | 29.4 °C | 30.73 mm |
| August | 10.1 °C | 29.1 °C | 28.19 mm |
| September | 6.1 °C | 22.7 °C | 26.16 mm |
| October | 0.6 °C | 14.3 °C | 21.84 mm |
| November | -4.5 °C | 6.3 °C | 14.48 mm |
| December | -9 °C | 1.2 °C | 6.6 mm |
| Annual | 0.3 °C | 14.2 °C | 321.29 mm |
| 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 4b : -31.7°C to -28.9°C |
| Plant Hardiness Zone - 2012 | Zone 4b : -31.7°C to -28.9°C |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |