Altadena, California has a Hot-Summer Mediterranean Climate climate (Köppen classification: Csa). Average annual temperatures range from 11.7 °C (low) to 24.8 °C (high). Annual precipitation averages 590.6 Millimeters. Altadena is located in USDA Plant Hardiness Zone 10b. The growing season typically runs from the last frost around Frost Rare through the first frost around Jan. 21 - Jan. 31.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 7.9 °C | 19.8 °C | 127 mm |
| February | 7.8 °C | 19.5 °C | 154.94 mm |
| March | 8.7 °C | 21.1 °C | 89.41 mm |
| April | 9.8 °C | 22.2 °C | 36.32 mm |
| May | 11.6 °C | 24.1 °C | 22.35 mm |
| June | 13.6 °C | 26.9 °C | 8.89 mm |
| July | 16.3 °C | 30.8 °C | 2.54 mm |
| August | 16.8 °C | 33.1 °C | 0.76 mm |
| September | 16.2 °C | 29.9 °C | 5.84 mm |
| October | 13.7 °C | 27 °C | 27.69 mm |
| November | 10.1 °C | 23.4 °C | 31.5 mm |
| December | 7.8 °C | 19.3 °C | 83.31 mm |
| Annual | 11.7 °C | 24.8 °C | 590.55 mm |
| Average First Frost Date | Jan. 21 - Jan. 31 |
| Average Last Frost Date | Frost Rare |
| Average Days With Frost | Frost Rare |
| Plant Hardiness Zone | Zone 10b : 1.7°C to 4.4°C |
| Plant Hardiness Zone - 2012 | Zone 10a : -1.1°C to 1.7°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Csa - Hot-Summer Mediterranean Climate |