Brentwood, California has a Warm-Summer Mediterranean Climate climate (Köppen classification: Csb). Average annual temperatures range from 49.9 °F (low) to 73.1 °F (high). Annual precipitation averages 13.7 Inches. Brentwood is located in USDA Plant Hardiness Zone 9b. The growing season typically runs from the last frost around Feb. 1 - Feb. 10 through the first frost around Dec. 11 - Dec. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 39.9 °F | 55.6 °F | 2.82 in. |
| February | 42.5 °F | 60.5 °F | 2.63 in. |
| March | 45.6 °F | 65.7 °F | 1.86 in. |
| April | 48.6 °F | 70.7 °F | 0.99 in. |
| May | 53.0 °F | 77.6 °F | 0.49 in. |
| June | 57.1 °F | 84.9 °F | 0.14 in. |
| July | 59.1 °F | 89.8 °F | 0.0 in. |
| August | 59.2 °F | 88.8 °F | 0.02 in. |
| September | 57.6 °F | 85.9 °F | 0.06 in. |
| October | 52.1 °F | 77.4 °F | 0.62 in. |
| November | 44.3 °F | 64.8 °F | 1.39 in. |
| December | 39.7 °F | 55.9 °F | 2.71 in. |
| Annual | 49.9 °F | 73.1 °F | 13.73 in. |
| Average First Frost Date | Dec. 11 - Dec. 20 |
| Average Last Frost Date | Feb. 1 - Feb. 10 |
| Average Days With Frost | 10-20 Days |
| Plant Hardiness Zone | Zone 9b : 25°F to 20°F |
| Plant Hardiness Zone - 2012 | Zone 9b : 25°F to 20°F |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Csb - Warm-Summer Mediterranean Climate |