Fairfax, South Dakota has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 2.3 °C (low) to 15 °C (high). Annual precipitation averages 680.2 Millimeters. Fairfax 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 Oct. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -11.8 °C | -0.4 °C | 11.18 mm |
| February | -9.9 °C | 2.1 °C | 18.54 mm |
| March | -4.8 °C | 8.3 °C | 32.51 mm |
| April | 1.3 °C | 14.2 °C | 82.8 mm |
| May | 7.5 °C | 20.6 °C | 105.41 mm |
| June | 13.7 °C | 26.2 °C | 106.43 mm |
| July | 16.9 °C | 30.2 °C | 81.53 mm |
| August | 15.6 °C | 28.9 °C | 79.5 mm |
| September | 10.3 °C | 24.3 °C | 73.91 mm |
| October | 2.7 °C | 16.3 °C | 52.58 mm |
| November | -4.2 °C | 8.2 °C | 20.32 mm |
| December | -9.8 °C | 1.2 °C | 15.49 mm |
| Annual | 2.3 °C | 15 °C | 680.2 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 5a : -28.9°C to -26.1°C |
| Plant Hardiness Zone - 2012 | Zone 5a : -28.9°C to -26.1°C |
| Current Drought Conditions | Moderate Drought |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |