Westmont, California has a Warm-Summer Mediterranean Climate climate (Köppen classification: Csb). Average annual temperatures range from 55.8 °F (low) to 72.7 °F (high). Annual precipitation averages 14.3 Inches. Westmont is located in USDA Plant Hardiness Zone 10b.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 48.7 °F | 66.7 °F | 3.38 in. |
| February | 49.4 °F | 66.4 °F | 3.68 in. |
| March | 51.3 °F | 67.3 °F | 2.31 in. |
| April | 53.3 °F | 70.2 °F | 0.7 in. |
| May | 56.8 °F | 71.9 °F | 0.28 in. |
| June | 60.1 °F | 74.6 °F | 0.06 in. |
| July | 63.2 °F | 79.2 °F | 0.04 in. |
| August | 63.9 °F | 81.0 °F | 0.02 in. |
| September | 62.8 °F | 80.3 °F | 0.12 in. |
| October | 58.8 °F | 76.9 °F | 0.57 in. |
| November | 52.8 °F | 71.6 °F | 0.74 in. |
| December | 48.3 °F | 66.5 °F | 2.37 in. |
| Annual | 55.8 °F | 72.7 °F | 14.27 in. |
| Average First Frost Date | No Frost |
| Average Last Frost Date | |
| Average Days With Frost | Frost Free |
| Plant Hardiness Zone | Zone 10b : 35°F to 30°F |
| Plant Hardiness Zone - 2012 | Zone 10b : 35°F to 30°F |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Csb - Warm-Summer Mediterranean Climate |