Diamond Bar, California has a Hot-Summer Mediterranean Climate climate (Köppen classification: Csa). Average annual temperatures range from 52.7 °F (low) to 77.5 °F (high). Annual precipitation averages 16.6 Inches. Diamond Bar is located in USDA Plant Hardiness Zone 10a.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 44.7 °F | 67.9 °F | 3.52 in. |
| February | 45.4 °F | 68.2 °F | 4.21 in. |
| March | 47.5 °F | 71.0 °F | 2.64 in. |
| April | 49.7 °F | 73.5 °F | 0.87 in. |
| May | 54.0 °F | 77.0 °F | 0.36 in. |
| June | 57.6 °F | 82.2 °F | 0.1 in. |
| July | 61.8 °F | 88.7 °F | 0.09 in. |
| August | 62.4 °F | 90.7 °F | 0.01 in. |
| September | 60.7 °F | 88.1 °F | 0.16 in. |
| October | 55.6 °F | 81.2 °F | 0.88 in. |
| November | 48.9 °F | 74.3 °F | 0.96 in. |
| December | 44.0 °F | 67.1 °F | 2.78 in. |
| Annual | 52.7 °F | 77.5 °F | 16.58 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 |