Fairmont, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 5 °C (low) to 15.6 °C (high). Annual precipitation averages 1013.7 Millimeters. Fairmont is located in USDA Plant Hardiness Zone 6a. 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 | -8.7 °C | -0.2 °C | 53.59 mm |
| February | -7.2 °C | 2 °C | 49.78 mm |
| March | -1.8 °C | 8.6 °C | 63.25 mm |
| April | 4 °C | 15.8 °C | 99.57 mm |
| May | 9.9 °C | 21.9 °C | 122.43 mm |
| June | 15.6 °C | 27.2 °C | 118.87 mm |
| July | 17.8 °C | 29.2 °C | 110.49 mm |
| August | 17.1 °C | 28.2 °C | 106.68 mm |
| September | 12.8 °C | 24.9 °C | 85.09 mm |
| October | 6.1 °C | 17.6 °C | 86.61 mm |
| November | 0 °C | 9.6 °C | 62.48 mm |
| December | -5.5 °C | 2.7 °C | 54.86 mm |
| Annual | 5 °C | 15.6 °C | 1013.7 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 11 - Apr. 20 |
| Average Days With Frost | 100-125 Days |
| Plant Hardiness Zone | Zone 6a : -23.3°C to -20.6°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 |