Alta, California has a Warm-Summer Mediterranean Climate climate (Köppen classification: Csb). Average annual temperatures range from 45.2 °F (low) to 66.1 °F (high). Annual precipitation averages 62.8 Inches. 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 | 35.1 °F | 49.8 °F | 10.8 in. |
| February | 34.7 °F | 51.4 °F | 10.44 in. |
| March | 36.2 °F | 55.6 °F | 9.57 in. |
| April | 39.2 °F | 60.6 °F | 5.41 in. |
| May | 45.7 °F | 69.0 °F | 3.33 in. |
| June | 53.1 °F | 78.8 °F | 1.0 in. |
| July | 60.6 °F | 86.6 °F | 0.08 in. |
| August | 60.9 °F | 86.4 °F | 0.13 in. |
| September | 55.2 °F | 81.2 °F | 0.55 in. |
| October | 47.6 °F | 69.6 °F | 3.07 in. |
| November | 39.2 °F | 55.9 °F | 6.5 in. |
| December | 34.5 °F | 48.1 °F | 11.91 in. |
| Annual | 45.2 °F | 66.1 °F | 62.79 in. |
| 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 : 20°F to 25°F |
| Plant Hardiness Zone - 2012 | Zone 8b : 15°F to 20°F |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Csb - Warm-Summer Mediterranean Climate |