Clayton, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 42.2 °F (low) to 62.1 °F (high). Annual precipitation averages 39.6 Inches. 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 | 17.3 °F | 34.0 °F | 1.86 in. |
| February | 20.9 °F | 39.1 °F | 1.93 in. |
| March | 30.5 °F | 50.7 °F | 2.52 in. |
| April | 41.4 °F | 62.9 °F | 4.02 in. |
| May | 52.8 °F | 73.0 °F | 5.17 in. |
| June | 62.2 °F | 82.0 °F | 4.83 in. |
| July | 65.6 °F | 85.7 °F | 4.06 in. |
| August | 63.2 °F | 84.1 °F | 3.7 in. |
| September | 54.6 °F | 78.2 °F | 3.47 in. |
| October | 43.3 °F | 65.6 °F | 3.24 in. |
| November | 32.3 °F | 51.5 °F | 2.68 in. |
| December | 22.6 °F | 38.9 °F | 2.08 in. |
| Annual | 42.2 °F | 62.1 °F | 39.56 in. |
| 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 : -10°F to -5°F |
| Plant Hardiness Zone - 2012 | Zone 5b : -15°F to -10°F |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |