Clayton, California has a Warm-Summer Mediterranean Climate climate (Köppen classification: Csb). Average annual temperatures range from 8.6 °C (low) to 21.9 °C (high). Annual precipitation averages 494.8 Millimeters. Clayton is located in USDA Plant Hardiness Zone 9b. The growing season typically runs from the last frost around Feb. 21 - Feb. 29 through the first frost around Dec. 11 - Dec. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 4 °C | 13.3 °C | 98.04 mm |
| February | 4.9 °C | 15.6 °C | 96.01 mm |
| March | 6 °C | 18.1 °C | 67.06 mm |
| April | 7.4 °C | 20.7 °C | 39.12 mm |
| May | 9.8 °C | 23.4 °C | 17.02 mm |
| June | 11.9 °C | 27.4 °C | 3.56 mm |
| July | 13.3 °C | 30 °C | 0.25 mm |
| August | 13.6 °C | 30 °C | 0.76 mm |
| September | 12.6 °C | 28.9 °C | 2.03 mm |
| October | 9.9 °C | 24.1 °C | 23.11 mm |
| November | 6.1 °C | 17.9 °C | 49.53 mm |
| December | 3.8 °C | 13.3 °C | 98.3 mm |
| Annual | 8.6 °C | 21.9 °C | 494.79 mm |
| Average First Frost Date | Dec. 11 - Dec. 20 |
| Average Last Frost Date | Feb. 21 - Feb. 29 |
| Average Days With Frost | 10-20 Days |
| Plant Hardiness Zone | Zone 9b : -3.9°C to -1.1°C |
| Plant Hardiness Zone - 2012 | Zone 9a : -6.7°C to -3.9°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Csb - Warm-Summer Mediterranean Climate |