Fairfax, South Dakota has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 36.1 °F (low) to 59 °F (high). Annual precipitation averages 26.8 Inches. 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 | 10.7 °F | 31.3 °F | 0.44 in. |
| February | 14.2 °F | 35.8 °F | 0.73 in. |
| March | 23.4 °F | 47.0 °F | 1.28 in. |
| April | 34.3 °F | 57.5 °F | 3.26 in. |
| May | 45.5 °F | 69.1 °F | 4.15 in. |
| June | 56.6 °F | 79.1 °F | 4.19 in. |
| July | 62.4 °F | 86.3 °F | 3.21 in. |
| August | 60.1 °F | 84.1 °F | 3.13 in. |
| September | 50.5 °F | 75.8 °F | 2.91 in. |
| October | 36.9 °F | 61.4 °F | 2.07 in. |
| November | 24.4 °F | 46.8 °F | 0.8 in. |
| December | 14.4 °F | 34.2 °F | 0.61 in. |
| Annual | 36.1 °F | 59 °F | 26.78 in. |
| 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 : -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 |