Fairfield, Iowa has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 4.9 °C (low) to 16.1 °C (high). Annual precipitation averages 975.4 Millimeters. Fairfield is located in USDA Plant Hardiness Zone 5b. The growing season typically runs from the last frost around Apr. 11 - Apr. 20 through the first frost around Oct. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -9.6 °C | -0.2 °C | 37.08 mm |
| February | -7.7 °C | 2.3 °C | 43.43 mm |
| March | -1.7 °C | 9.6 °C | 58.42 mm |
| April | 4.4 °C | 17 °C | 95.76 mm |
| May | 10.9 °C | 22.6 °C | 137.41 mm |
| June | 16.5 °C | 27.8 °C | 128.52 mm |
| July | 18.5 °C | 29.9 °C | 104.9 mm |
| August | 17.1 °C | 28.9 °C | 101.35 mm |
| September | 12.2 °C | 25.3 °C | 91.95 mm |
| October | 5.7 °C | 18.2 °C | 74.42 mm |
| November | -0.7 °C | 9.7 °C | 58.42 mm |
| December | -6.3 °C | 2.6 °C | 43.69 mm |
| Annual | 4.9 °C | 16.1 °C | 975.35 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 11 - Apr. 20 |
| Average Days With Frost | 125-150 Days |
| Plant Hardiness Zone | Zone 5b : -26.1°C to -23.3°C |
| Plant Hardiness Zone - 2012 | Zone 5b : -26.1°C to -23.3°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |