Helmville, Montana has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from -3.2 °C (low) to 12.9 °C (high). Annual precipitation averages 351 Millimeters. Helmville is located in USDA Plant Hardiness Zone 4b. The growing season typically runs from the last frost around May 1 - May 10 through the first frost around Sep. 21 - Sep. 30.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -11.9 °C | -0.3 °C | 25.4 mm |
| February | -11.1 °C | 2.2 °C | 21.59 mm |
| March | -7.1 °C | 7.2 °C | 17.27 mm |
| April | -3.3 °C | 12.1 °C | 26.42 mm |
| May | 0.6 °C | 17.7 °C | 43.69 mm |
| June | 4.2 °C | 21.7 °C | 55.88 mm |
| July | 6.3 °C | 27.9 °C | 24.13 mm |
| August | 5.3 °C | 27.7 °C | 24.38 mm |
| September | 1.4 °C | 21.8 °C | 28.19 mm |
| October | -3.3 °C | 13.1 °C | 27.18 mm |
| November | -7.7 °C | 4.6 °C | 29.21 mm |
| December | -11.8 °C | -0.7 °C | 27.69 mm |
| Annual | -3.2 °C | 12.9 °C | 351.03 mm |
| Average First Frost Date | Sep. 21 - Sep. 30 |
| Average Last Frost Date | May 1 - May 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 | Normal |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |