Hardin, Montana has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 0.9 °C (low) to 16.9 °C (high). Annual precipitation averages 333.8 Millimeters. Hardin 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 Oct. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -11.1 °C | 2.2 °C | 11.68 mm |
| February | -9.4 °C | 4.6 °C | 10.92 mm |
| March | -4.5 °C | 10.7 °C | 17.02 mm |
| April | 0.4 °C | 16.6 °C | 39.62 mm |
| May | 5.7 °C | 21.6 °C | 61.98 mm |
| June | 10.6 °C | 27.2 °C | 47.75 mm |
| July | 13.8 °C | 32.4 °C | 33.53 mm |
| August | 12.6 °C | 31.8 °C | 19.56 mm |
| September | 7.4 °C | 26.2 °C | 32.51 mm |
| October | 0.8 °C | 17.6 °C | 33.02 mm |
| November | -5.1 °C | 9 °C | 13.72 mm |
| December | -10.2 °C | 2.9 °C | 12.45 mm |
| Annual | 0.9 °C | 16.9 °C | 333.76 mm |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| 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 | Moderate Drought |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |