Diamond Bar, California has a Hot-Summer Mediterranean Climate climate (Köppen classification: Csa). Average annual temperatures range from 11.5 °C (low) to 25.3 °C (high). Annual precipitation averages 421.1 Millimeters. Diamond Bar is located in USDA Plant Hardiness Zone 10a.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 7.1 °C | 19.9 °C | 89.41 mm |
| February | 7.4 °C | 20.1 °C | 106.93 mm |
| March | 8.6 °C | 21.7 °C | 67.06 mm |
| April | 9.8 °C | 23.1 °C | 22.1 mm |
| May | 12.2 °C | 25 °C | 9.14 mm |
| June | 14.2 °C | 27.9 °C | 2.54 mm |
| July | 16.6 °C | 31.5 °C | 2.29 mm |
| August | 16.9 °C | 32.6 °C | 0.25 mm |
| September | 15.9 °C | 31.2 °C | 4.06 mm |
| October | 13.1 °C | 27.3 °C | 22.35 mm |
| November | 9.4 °C | 23.5 °C | 24.38 mm |
| December | 6.7 °C | 19.5 °C | 70.61 mm |
| Annual | 11.5 °C | 25.3 °C | 421.12 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 |