Clayton, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 5.7 °C (low) to 16.7 °C (high). Annual precipitation averages 1004.8 Millimeters. Clayton is located in USDA Plant Hardiness Zone 6a. The growing season typically runs from the last frost around Apr. 1 - Apr. 10 through the first frost around Oct. 21 - Oct. 31.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -8.2 °C | 1.1 °C | 47.24 mm |
| February | -6.2 °C | 3.9 °C | 49.02 mm |
| March | -0.8 °C | 10.4 °C | 64.01 mm |
| April | 5.2 °C | 17.2 °C | 102.11 mm |
| May | 11.6 °C | 22.8 °C | 131.32 mm |
| June | 16.8 °C | 27.8 °C | 122.68 mm |
| July | 18.7 °C | 29.8 °C | 103.12 mm |
| August | 17.3 °C | 28.9 °C | 93.98 mm |
| September | 12.6 °C | 25.7 °C | 88.14 mm |
| October | 6.3 °C | 18.7 °C | 82.3 mm |
| November | 0.2 °C | 10.8 °C | 68.07 mm |
| December | -5.2 °C | 3.8 °C | 52.83 mm |
| Annual | 5.7 °C | 16.7 °C | 1004.82 mm |
| Average First Frost Date | Oct. 21 - Oct. 31 |
| Average Last Frost Date | Apr. 1 - Apr. 10 |
| 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 |