Brentwood, California has a Warm-Summer Mediterranean Climate climate (Köppen classification: Csb). Average annual temperatures range from 9.9 °C (low) to 22.8 °C (high). Annual precipitation averages 348.8 Millimeters. 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 | 4.4 °C | 13.1 °C | 71.63 mm |
| February | 5.8 °C | 15.8 °C | 66.8 mm |
| March | 7.6 °C | 18.7 °C | 47.24 mm |
| April | 9.2 °C | 21.5 °C | 25.15 mm |
| May | 11.7 °C | 25.3 °C | 12.45 mm |
| June | 13.9 °C | 29.4 °C | 3.56 mm |
| July | 15.1 °C | 32.1 °C | 0 mm |
| August | 15.1 °C | 31.6 °C | 0.51 mm |
| September | 14.2 °C | 29.9 °C | 1.52 mm |
| October | 11.2 °C | 25.2 °C | 15.75 mm |
| November | 6.8 °C | 18.2 °C | 35.31 mm |
| December | 4.3 °C | 13.3 °C | 68.83 mm |
| Annual | 9.9 °C | 22.8 °C | 348.75 mm |
| 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 : -3.9°C to -1.1°C |
| Plant Hardiness Zone - 2012 | Zone 9b : -3.9°C to -1.1°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Csb - Warm-Summer Mediterranean Climate |