Mellette, South Dakota has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Annual precipitation averages 573 Millimeters. Mellette 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 | -16.6 °C | -5.4 °C | 13.21 mm |
| February | -14 °C | -2.2 °C | 16 mm |
| March | -7.3 °C | 4.7 °C | 24.13 mm |
| April | -0.4 °C | 13.2 °C | 54.86 mm |
| May | 6.9 °C | 20.4 °C | 85.34 mm |
| June | 13 °C | 25.7 °C | 92.96 mm |
| July | 15.6 °C | 28.6 °C | 83.06 mm |
| August | 13.9 °C | 27.9 °C | 60.96 mm |
| September | 8.4 °C | 23.4 °C | 53.34 mm |
| October | 1 °C | 15.1 °C | 54.1 mm |
| November | -6.6 °C | 5.4 °C | 18.8 mm |
| December | -13.3 °C | -2.6 °C | 16.26 mm |
| Annual | 0 °C | 12.9 °C | 573.02 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 | Abnormally Dry |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |