Fairfax, Iowa has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 38.8 °F (low) to 58.8 °F (high). Annual precipitation averages 37.3 Inches. Fairfax is located in USDA Plant Hardiness Zone 5a. The growing season typically runs from the last frost around Apr. 21 - Apr. 30 through the first frost around Oct. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 11.8 °F | 28.4 °F | 1.08 in. |
| February | 15.5 °F | 32.9 °F | 1.25 in. |
| March | 26.7 °F | 46.1 °F | 2.11 in. |
| April | 37.8 °F | 60.3 °F | 3.71 in. |
| May | 49.9 °F | 71.3 °F | 4.47 in. |
| June | 60.4 °F | 80.6 °F | 5.52 in. |
| July | 63.6 °F | 83.7 °F | 4.47 in. |
| August | 61.0 °F | 81.9 °F | 4.33 in. |
| September | 52.4 °F | 75.9 °F | 3.65 in. |
| October | 40.3 °F | 62.8 °F | 2.88 in. |
| November | 28.3 °F | 47.2 °F | 2.19 in. |
| December | 17.9 °F | 33.9 °F | 1.59 in. |
| Annual | 38.8 °F | 58.8 °F | 37.25 in. |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | Apr. 21 - Apr. 30 |
| Average Days With Frost | 125-150 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 | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |