Adair, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 5.1 °C (low) to 16.6 °C (high). Annual precipitation averages 988.6 Millimeters. Adair 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 | -9 °C | 0.6 °C | 47.5 mm |
| February | -7 °C | 3.2 °C | 48.26 mm |
| March | -1.4 °C | 10.1 °C | 62.74 mm |
| April | 4.5 °C | 17.3 °C | 98.55 mm |
| May | 11.2 °C | 23.2 °C | 128.52 mm |
| June | 16.4 °C | 28 °C | 123.19 mm |
| July | 18.2 °C | 29.7 °C | 102.36 mm |
| August | 16.8 °C | 28.8 °C | 89.92 mm |
| September | 12.2 °C | 25.7 °C | 92.71 mm |
| October | 5.7 °C | 18.8 °C | 78.23 mm |
| November | -0.4 °C | 10.4 °C | 66.29 mm |
| December | -5.8 °C | 3.4 °C | 50.29 mm |
| Annual | 5.1 °C | 16.6 °C | 988.56 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 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 |