Greenhorn, California has a Warm-Summer Mediterranean Climate climate (Köppen classification: Csb). Average annual temperatures range from 1.3 °C (low) to 17 °C (high). Annual precipitation averages 1169.2 Millimeters. Greenhorn is located in USDA Plant Hardiness Zone 7a. The growing season typically runs from the last frost around Jun. 1 - Jun. 10 through the first frost around Sep.11 - Sep. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -4.6 °C | 6.5 °C | 216.92 mm |
| February | -4.1 °C | 8.2 °C | 193.55 mm |
| March | -2.3 °C | 10.9 °C | 171.2 mm |
| April | -0.6 °C | 14.2 °C | 98.81 mm |
| May | 2.9 °C | 19.2 °C | 59.44 mm |
| June | 6.2 °C | 24.7 °C | 21.08 mm |
| July | 9.5 °C | 29.7 °C | 4.32 mm |
| August | 8.6 °C | 29.3 °C | 4.32 mm |
| September | 5.6 °C | 26.1 °C | 15.75 mm |
| October | 1.4 °C | 19.1 °C | 58.17 mm |
| November | -2.2 °C | 10.7 °C | 110.24 mm |
| December | -4.6 °C | 5.7 °C | 215.39 mm |
| Annual | 1.3 °C | 17 °C | 1169.19 mm |
| Average First Frost Date | Sep.11 - Sep. 20 |
| Average Last Frost Date | Jun. 1 - Jun. 10 |
| Average Days With Frost | 125-150 Days |
| Plant Hardiness Zone | Zone 7a : -17.8°C to -15°C |
| Plant Hardiness Zone - 2012 | Zone 7b : -15°C to -12.2°C |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Csb - Warm-Summer Mediterranean Climate |