Green Grass, South Dakota has a Cold Semi-Arid Climate climate (Köppen classification: BSk). Average annual temperatures range from 1 °C (low) to 14.3 °C (high). Annual precipitation averages 458 Millimeters. Green Grass 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 Oct. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -13.8 °C | -2.8 °C | 9.91 mm |
| February | -12.1 °C | -0.4 °C | 14.22 mm |
| March | -6.2 °C | 6.6 °C | 21.84 mm |
| April | 0.1 °C | 14.1 °C | 43.18 mm |
| May | 6.8 °C | 20.2 °C | 71.12 mm |
| June | 12.8 °C | 26.1 °C | 83.82 mm |
| July | 16.1 °C | 30.4 °C | 65.79 mm |
| August | 14.6 °C | 30 °C | 47.5 mm |
| September | 9.2 °C | 24.8 °C | 35.31 mm |
| October | 1.8 °C | 15.5 °C | 40.64 mm |
| November | -5.5 °C | 6.8 °C | 12.19 mm |
| December | -11.4 °C | -0.3 °C | 12.45 mm |
| Annual | 1 °C | 14.3 °C | 457.97 mm |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | May 1 - May 10 |
| 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 | BSk - Cold Semi-Arid Climate |