Union, Mississippi has a Humid Subtropical Climate climate (Köppen classification: Cfa). Average annual temperatures range from 11.4 °C (low) to 24.3 °C (high). Annual precipitation averages 1518.9 Millimeters. Union is located in USDA Plant Hardiness Zone 8b. The growing season typically runs from the last frost around Mar. 21 - Mar. 31 through the first frost around Nov. 1 - Nov. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 1.6 °C | 13.6 °C | 151.38 mm |
| February | 3.3 °C | 16.2 °C | 144.78 mm |
| March | 6.7 °C | 20.4 °C | 146.56 mm |
| April | 10.6 °C | 24.4 °C | 156.21 mm |
| May | 15.5 °C | 28.3 °C | 108.71 mm |
| June | 19.7 °C | 32 °C | 114.81 mm |
| July | 21.2 °C | 33.2 °C | 138.68 mm |
| August | 20.7 °C | 32.9 °C | 115.82 mm |
| September | 17.6 °C | 30.7 °C | 89.66 mm |
| October | 11.2 °C | 25.5 °C | 93.47 mm |
| November | 5.4 °C | 19.3 °C | 117.86 mm |
| December | 2.7 °C | 14.9 °C | 140.97 mm |
| Annual | 11.4 °C | 24.3 °C | 1518.91 mm |
| Average First Frost Date | Nov. 1 - Nov. 10 |
| Average Last Frost Date | Mar. 21 - Mar. 31 |
| Average Days With Frost | 40-50 Days |
| Plant Hardiness Zone | Zone 8b : -9.4°C to -6.7°C |
| Plant Hardiness Zone - 2012 | Zone 8a : -12.2°C to -9.4°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Cfa - Humid Subtropical Climate |