Walnut, California has a Hot-Summer Mediterranean Climate climate (Köppen classification: Csa). Average annual temperatures range from 11.8 °C (low) to 25.8 °C (high). Annual precipitation averages 409.7 Millimeters. Walnut is located in USDA Plant Hardiness Zone 10a.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 7.3 °C | 20.4 °C | 98.81 mm |
| February | 7.7 °C | 20.5 °C | 104.9 mm |
| March | 8.9 °C | 21.9 °C | 59.18 mm |
| April | 10.3 °C | 23.7 °C | 19.3 mm |
| May | 12.7 °C | 25.5 °C | 9.4 mm |
| June | 14.7 °C | 28.6 °C | 3.05 mm |
| July | 16.9 °C | 32.2 °C | 1.27 mm |
| August | 17.2 °C | 33.3 °C | 0.51 mm |
| September | 16.2 °C | 31.8 °C | 3.56 mm |
| October | 13.3 °C | 28 °C | 16.76 mm |
| November | 9.6 °C | 23.8 °C | 24.64 mm |
| December | 6.9 °C | 20 °C | 68.33 mm |
| Annual | 11.8 °C | 25.8 °C | 409.71 mm |
| Average First Frost Date | No Frost |
| Average Last Frost Date | |
| Average Days With Frost | Frost Free |
| Plant Hardiness Zone | Zone 10a : -1.1°C to 1.7°C |
| Plant Hardiness Zone - 2012 | Zone 10a : -1.1°C to 1.7°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Csa - Hot-Summer Mediterranean Climate |