Posey, California has a Hot Semi-Arid Climate climate (Köppen classification: BSh). Average annual temperatures range from 7.3 °C (low) to 21 °C (high). Annual precipitation averages 569.2 Millimeters. Posey is located in USDA Plant Hardiness Zone 9a. The growing season typically runs from the last frost around May 11 - May 20 through the first frost around Oct. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 1.4 °C | 13.1 °C | 107.44 mm |
| February | 1.8 °C | 12.7 °C | 115.32 mm |
| March | 2.8 °C | 15.1 °C | 87.88 mm |
| April | 4.4 °C | 17.3 °C | 50.29 mm |
| May | 7.8 °C | 22.3 °C | 21.84 mm |
| June | 11.6 °C | 27.8 °C | 8.13 mm |
| July | 15.7 °C | 31.9 °C | 1.52 mm |
| August | 15.4 °C | 31.8 °C | 2.29 mm |
| September | 12.9 °C | 28.8 °C | 3.56 mm |
| October | 8.3 °C | 22.5 °C | 25.15 mm |
| November | 4.3 °C | 16.7 °C | 50.8 mm |
| December | 1.4 °C | 12.3 °C | 95 mm |
| Annual | 7.3 °C | 21 °C | 569.22 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | May 11 - May 20 |
| Average Days With Frost | 75-100 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 | BSh - Hot Semi-Arid Climate |