Fallbrook, California has a Cold Semi-Arid Climate climate (Köppen classification: BSk). Average annual temperatures range from 11.8 °C (low) to 23.9 °C (high). Annual precipitation averages 410.2 Millimeters. Fallbrook is located in USDA Plant Hardiness Zone 10b. The growing season typically runs from the last frost around Jan. 21 - Jan. 31 through the first frost around Jan. 1 - Jan. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 8.1 °C | 19.7 °C | 93.47 mm |
| February | 8.2 °C | 19.4 °C | 102.11 mm |
| March | 8.8 °C | 19.8 °C | 57.15 mm |
| April | 9.8 °C | 21.6 °C | 28.19 mm |
| May | 11.9 °C | 22.9 °C | 8.38 mm |
| June | 13.8 °C | 25.8 °C | 2.29 mm |
| July | 16 °C | 28.7 °C | 2.29 mm |
| August | 16.7 °C | 30.3 °C | 0.76 mm |
| September | 16.1 °C | 29.8 °C | 3.56 mm |
| October | 13.8 °C | 26.7 °C | 15.75 mm |
| November | 10.6 °C | 22.8 °C | 28.7 mm |
| December | 8 °C | 19.4 °C | 67.56 mm |
| Annual | 11.8 °C | 23.9 °C | 410.21 mm |
| Average First Frost Date | Jan. 1 - Jan. 10 |
| Average Last Frost Date | Jan. 21 - Jan. 31 |
| Average Days With Frost | Frost Rare |
| Plant Hardiness Zone | Zone 10b : 1.7°C to 4.4°C |
| Plant Hardiness Zone - 2012 | Zone 10b : 1.7°C to 4.4°C |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | BSk - Cold Semi-Arid Climate |