Union Valley, Texas has a Humid Subtropical Climate climate (Köppen classification: Cfa). Average annual temperatures range from 12.4 °C (low) to 24.5 °C (high). Annual precipitation averages 1076.2 Millimeters. Union Valley is located in USDA Plant Hardiness Zone 8b. The growing season typically runs from the last frost around Mar. 11 - Mar. 20 through the first frost around Nov. 11 - Nov. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 1.4 °C | 13.3 °C | 71.37 mm |
| February | 3.4 °C | 15.6 °C | 79.76 mm |
| March | 7.4 °C | 19.7 °C | 98.55 mm |
| April | 11.6 °C | 23.9 °C | 94.23 mm |
| May | 16.9 °C | 28 °C | 124.97 mm |
| June | 21.3 °C | 32.4 °C | 99.31 mm |
| July | 23.1 °C | 34.6 °C | 55.63 mm |
| August | 22.7 °C | 35.1 °C | 63.5 mm |
| September | 18.8 °C | 31.5 °C | 80.01 mm |
| October | 12.7 °C | 25.8 °C | 125.98 mm |
| November | 6.9 °C | 19.2 °C | 90.68 mm |
| December | 2.5 °C | 14.3 °C | 92.2 mm |
| Annual | 12.4 °C | 24.5 °C | 1076.19 mm |
| Average First Frost Date | Nov. 11 - Nov. 20 |
| Average Last Frost Date | Mar. 11 - Mar. 20 |
| 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 |