Walnut, California has a Hot-Summer Mediterranean Climate climate (Köppen classification: Csa). Average annual temperatures range from 53.3 °F (low) to 78.5 °F (high). Annual precipitation averages 16.1 Inches. Walnut is located in USDA Plant Hardiness Zone 10a.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 45.1 °F | 68.7 °F | 3.89 in. |
| February | 45.9 °F | 68.9 °F | 4.13 in. |
| March | 48.0 °F | 71.5 °F | 2.33 in. |
| April | 50.5 °F | 74.6 °F | 0.76 in. |
| May | 54.9 °F | 77.9 °F | 0.37 in. |
| June | 58.4 °F | 83.4 °F | 0.12 in. |
| July | 62.5 °F | 90.0 °F | 0.05 in. |
| August | 62.9 °F | 91.9 °F | 0.02 in. |
| September | 61.1 °F | 89.3 °F | 0.14 in. |
| October | 56.0 °F | 82.4 °F | 0.66 in. |
| November | 49.2 °F | 74.8 °F | 0.97 in. |
| December | 44.5 °F | 68.0 °F | 2.69 in. |
| Annual | 53.3 °F | 78.5 °F | 16.13 in. |
| Average First Frost Date | No Frost |
| Average Last Frost Date | |
| Average Days With Frost | Frost Free |
| Plant Hardiness Zone | Zone 10a : 30°F to 25°F |
| Plant Hardiness Zone - 2012 | Zone 10a : 30°F to 25°F |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Csa - Hot-Summer Mediterranean Climate |