Keystone, South Dakota has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 0.4 °C (low) to 14.2 °C (high). Annual precipitation averages 577.6 Millimeters. Keystone is located in USDA Plant Hardiness Zone 5a. 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 | -9.9 °C | 3.3 °C | 12.19 mm |
| February | -9.8 °C | 3.7 °C | 18.03 mm |
| March | -5.7 °C | 8.2 °C | 31.75 mm |
| April | -1.3 °C | 11.8 °C | 62.48 mm |
| May | 4.1 °C | 16.9 °C | 112.27 mm |
| June | 9.4 °C | 23 °C | 89.41 mm |
| July | 13.1 °C | 27.4 °C | 81.79 mm |
| August | 11.9 °C | 26.9 °C | 58.17 mm |
| September | 7 °C | 22.4 °C | 40.39 mm |
| October | 0.5 °C | 14.4 °C | 42.16 mm |
| November | -5.1 °C | 8.2 °C | 16.26 mm |
| December | -9.4 °C | 3.7 °C | 12.7 mm |
| Annual | 0.4 °C | 14.2 °C | 577.6 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 5a : -28.9°C to -26.1°C |
| Plant Hardiness Zone - 2012 | Zone 5a : -28.9°C to -26.1°C |
| Current Drought Conditions | Extreme Drought |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |