Keystone, South Dakota has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 32.7 °F (low) to 57.5 °F (high). Annual precipitation averages 22.7 Inches. 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 | 14.1 °F | 38.0 °F | 0.48 in. |
| February | 14.3 °F | 38.7 °F | 0.71 in. |
| March | 21.8 °F | 46.7 °F | 1.25 in. |
| April | 29.6 °F | 53.3 °F | 2.46 in. |
| May | 39.4 °F | 62.5 °F | 4.42 in. |
| June | 48.9 °F | 73.4 °F | 3.52 in. |
| July | 55.5 °F | 81.4 °F | 3.22 in. |
| August | 53.5 °F | 80.5 °F | 2.29 in. |
| September | 44.6 °F | 72.3 °F | 1.59 in. |
| October | 32.9 °F | 58.0 °F | 1.66 in. |
| November | 22.9 °F | 46.8 °F | 0.64 in. |
| December | 15.1 °F | 38.7 °F | 0.5 in. |
| Annual | 32.7 °F | 57.5 °F | 22.74 in. |
| 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 : -20°F to -15°F |
| Plant Hardiness Zone - 2012 | Zone 5a : -20°F to -15°F |
| Current Drought Conditions | Extreme Drought |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |