Stephan, South Dakota has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 0.6 °C (low) to 14.3 °C (high). Annual precipitation averages 529.9 Millimeters. Stephan 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 | -14.6 °C | -2.8 °C | 11.18 mm |
| February | -12.3 °C | -0.1 °C | 15.75 mm |
| March | -6.4 °C | 6.8 °C | 22.1 mm |
| April | -0.3 °C | 14.2 °C | 52.83 mm |
| May | 6.4 °C | 20.4 °C | 80.52 mm |
| June | 12.5 °C | 26.2 °C | 93.47 mm |
| July | 15.4 °C | 30.2 °C | 70.36 mm |
| August | 14.2 °C | 29.2 °C | 57.4 mm |
| September | 8.9 °C | 24.8 °C | 51.05 mm |
| October | 1.3 °C | 15.9 °C | 46.74 mm |
| November | -6.2 °C | 6.9 °C | 14.99 mm |
| December | -12 °C | -0.4 °C | 13.46 mm |
| Annual | 0.6 °C | 14.3 °C | 529.85 mm |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | 125-150 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 | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |