Fullerton, California has a Hot-Summer Mediterranean Climate climate (Köppen classification: Csa). Average annual temperatures range from 12.7 °C (low) to 24.4 °C (high). Annual precipitation averages 331.5 Millimeters. Fullerton is located in USDA Plant Hardiness Zone 10b.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 8.1 °C | 20.3 °C | 79.25 mm |
| February | 8.6 °C | 20.3 °C | 85.34 mm |
| March | 10 °C | 21.1 °C | 49.28 mm |
| April | 11.2 °C | 22.9 °C | 16.26 mm |
| May | 13.7 °C | 24 °C | 6.86 mm |
| June | 15.7 °C | 26 °C | 2.03 mm |
| July | 17.6 °C | 28.9 °C | 1.02 mm |
| August | 17.9 °C | 29.9 °C | 0 mm |
| September | 16.9 °C | 29.5 °C | 3.05 mm |
| October | 14.3 °C | 26.9 °C | 12.45 mm |
| November | 10.4 °C | 23.2 °C | 19.56 mm |
| December | 7.6 °C | 20 °C | 56.39 mm |
| Annual | 12.7 °C | 24.4 °C | 331.49 mm |
| Average First Frost Date | No Frost |
| Average Last Frost Date | |
| Average Days With Frost | Frost Free |
| 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 | Normal |
| Köppen Climate Classification | Csa - Hot-Summer Mediterranean Climate |