Alta, California has a Warm-Summer Mediterranean Climate climate (Köppen classification: Csb). Average annual temperatures range from 7.3 °C (low) to 18.9 °C (high). Annual precipitation averages 1594.9 Millimeters. Alta is located in USDA Plant Hardiness Zone 9a. The growing season typically runs from the last frost around Apr. 21 - Apr. 30 through the first frost around Nov. 1 - Nov. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 1.7 °C | 9.9 °C | 274.32 mm |
| February | 1.5 °C | 10.8 °C | 265.18 mm |
| March | 2.3 °C | 13.1 °C | 243.08 mm |
| April | 4 °C | 15.9 °C | 137.41 mm |
| May | 7.6 °C | 20.6 °C | 84.58 mm |
| June | 11.7 °C | 26 °C | 25.4 mm |
| July | 15.9 °C | 30.3 °C | 2.03 mm |
| August | 16.1 °C | 30.2 °C | 3.3 mm |
| September | 12.9 °C | 27.3 °C | 13.97 mm |
| October | 8.7 °C | 20.9 °C | 77.98 mm |
| November | 4 °C | 13.3 °C | 165.1 mm |
| December | 1.4 °C | 8.9 °C | 302.51 mm |
| Annual | 7.3 °C | 18.9 °C | 1594.86 mm |
| Average First Frost Date | Nov. 1 - Nov. 10 |
| Average Last Frost Date | Apr. 21 - Apr. 30 |
| Average Days With Frost | 50-75 Days |
| Plant Hardiness Zone | Zone 9a : -6.7°C to -3.9°C |
| Plant Hardiness Zone - 2012 | Zone 8b : -9.4°C to -6.7°C |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Csb - Warm-Summer Mediterranean Climate |