Hecla, South Dakota has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from -0.2 °C (low) to 11.8 °C (high). Annual precipitation averages 582.7 Millimeters. Hecla is located in USDA Plant Hardiness Zone 4a. 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 | -17.2 °C | -6.7 °C | 13.21 mm |
| February | -14.8 °C | -3.9 °C | 14.73 mm |
| March | -7.9 °C | 3.2 °C | 22.86 mm |
| April | -0.6 °C | 12.3 °C | 44.2 mm |
| May | 6.9 °C | 19.8 °C | 84.07 mm |
| June | 13.1 °C | 25 °C | 101.35 mm |
| July | 15.3 °C | 27.8 °C | 91.44 mm |
| August | 13.7 °C | 27.1 °C | 60.71 mm |
| September | 8.3 °C | 22.5 °C | 63.5 mm |
| October | 0.9 °C | 14 °C | 53.09 mm |
| November | -6.7 °C | 4.1 °C | 17.53 mm |
| December | -13.3 °C | -3.4 °C | 16 mm |
| Annual | -0.2 °C | 11.8 °C | 582.69 mm |
| Average First Frost Date | Sep. 21 - Sep. 30 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | 150-180 Days |
| Plant Hardiness Zone | Zone 4a : -34.4°C to -31.7°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 |