Clayton, Missouri has a Humid Subtropical Climate climate (Köppen classification: Cfa). Average annual temperatures range from 8.9 °C (low) to 19.2 °C (high). Annual precipitation averages 1118.6 Millimeters. Clayton is located in USDA Plant Hardiness Zone 7a. 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 | -4.3 °C | 4.7 °C | 68.58 mm |
| February | -2.6 °C | 7.7 °C | 59.44 mm |
| March | 2.4 °C | 13.4 °C | 89.15 mm |
| April | 8.4 °C | 19.9 °C | 119.13 mm |
| May | 14.4 °C | 24.9 °C | 131.83 mm |
| June | 19.4 °C | 29.7 °C | 116.84 mm |
| July | 21.4 °C | 31.6 °C | 104.14 mm |
| August | 20.4 °C | 30.9 °C | 96.27 mm |
| September | 15.8 °C | 27.2 °C | 85.09 mm |
| October | 9.6 °C | 20.8 °C | 86.61 mm |
| November | 3.1 °C | 12.9 °C | 91.44 mm |
| December | -1.6 °C | 7.1 °C | 70.1 mm |
| Annual | 8.9 °C | 19.2 °C | 1118.62 mm |
| Average First Frost Date | Oct. 21 - Oct. 31 |
| Average Last Frost Date | Apr. 1 - Apr. 10 |
| Average Days With Frost | 75-100 Days |
| Plant Hardiness Zone | Zone 7a : -17.8°C to -15°C |
| Plant Hardiness Zone - 2012 | Zone 6b : -20.6°C to -17.8°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Cfa - Humid Subtropical Climate |