Union, South Carolina has a Humid Subtropical Climate climate (Köppen classification: Cfa). Average annual temperatures range from 9.6 °C (low) to 22.8 °C (high). Annual precipitation averages 1158.7 Millimeters. Union is located in USDA Plant Hardiness Zone 8a. The growing season typically runs from the last frost around Apr. 1 - Apr. 10 through the first frost around Oct. 21 - Oct. 31.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -0.7 °C | 11.9 °C | 102.87 mm |
| February | 0.7 °C | 14.1 °C | 91.69 mm |
| March | 4 °C | 18.4 °C | 108.71 mm |
| April | 8.6 °C | 23.4 °C | 92.96 mm |
| May | 13.8 °C | 27.3 °C | 85.6 mm |
| June | 18.5 °C | 30.9 °C | 108.2 mm |
| July | 20.6 °C | 32.8 °C | 91.69 mm |
| August | 19.9 °C | 31.8 °C | 103.38 mm |
| September | 16.4 °C | 28.7 °C | 95.76 mm |
| October | 9.4 °C | 23.3 °C | 82.8 mm |
| November | 3.4 °C | 17.6 °C | 89.41 mm |
| December | 0.7 °C | 13.2 °C | 105.66 mm |
| Annual | 9.6 °C | 22.8 °C | 1158.73 mm |
| Average First Frost Date | Oct. 21 - Oct. 31 |
| Average Last Frost Date | Apr. 1 - Apr. 10 |
| Average Days With Frost | 50-75 Days |
| Plant Hardiness Zone | Zone 8a : -12.2°C to -9.4°C |
| Plant Hardiness Zone - 2012 | Zone 7b : -15°C to -12.2°C |
| Current Drought Conditions | Moderate Drought |
| Köppen Climate Classification | Cfa - Humid Subtropical Climate |