Hartley, California has a Hot-Summer Mediterranean Climate climate (Köppen classification: Csa). Average annual temperatures range from 48.6 °F (low) to 74.4 °F (high). Annual precipitation averages 25 Inches. Hartley is located in USDA Plant Hardiness Zone 9b. The growing season typically runs from the last frost around Feb. 1 - Feb. 10 through the first frost around Dec. 1 - Dec. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 38.6 °F | 56.5 °F | 5.3 in. |
| February | 41.0 °F | 61.2 °F | 5.33 in. |
| March | 43.9 °F | 66.1 °F | 3.42 in. |
| April | 46.8 °F | 71.3 °F | 1.42 in. |
| May | 51.8 °F | 78.8 °F | 0.78 in. |
| June | 56.4 °F | 86.7 °F | 0.16 in. |
| July | 58.7 °F | 91.9 °F | 0.0 in. |
| August | 57.8 °F | 90.9 °F | 0.02 in. |
| September | 56.2 °F | 88.1 °F | 0.07 in. |
| October | 50.6 °F | 78.8 °F | 0.98 in. |
| November | 43.1 °F | 65.6 °F | 2.25 in. |
| December | 38.4 °F | 56.6 °F | 5.23 in. |
| Annual | 48.6 °F | 74.4 °F | 24.96 in. |
| Average First Frost Date | Dec. 1 - Dec. 10 |
| Average Last Frost Date | Feb. 1 - Feb. 10 |
| Average Days With Frost | 10-20 Days |
| Plant Hardiness Zone | Zone 9b : 25°F to 20°F |
| Plant Hardiness Zone - 2012 | Zone 9b : 25°F to 20°F |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Csa - Hot-Summer Mediterranean Climate |