Union, Missouri has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 7.2 °C (low) to 19.3 °C (high). Annual precipitation averages 1131.6 Millimeters. Union is located in USDA Plant Hardiness Zone 6b. The growing season typically runs from the last frost around Apr. 11 - Apr. 20 through the first frost around Oct. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -5.7 °C | 4.8 °C | 62.99 mm |
| February | -3.8 °C | 7.9 °C | 60.96 mm |
| March | 0.9 °C | 13.6 °C | 93.98 mm |
| April | 6.7 °C | 20.3 °C | 122.43 mm |
| May | 12.6 °C | 24.8 °C | 135.64 mm |
| June | 17.6 °C | 29.4 °C | 110.74 mm |
| July | 19.9 °C | 31.6 °C | 111.76 mm |
| August | 18.6 °C | 31 °C | 94.74 mm |
| September | 13.9 °C | 27.3 °C | 96.01 mm |
| October | 7.3 °C | 20.9 °C | 84.84 mm |
| November | 1.4 °C | 13.4 °C | 86.87 mm |
| December | -3.3 °C | 7.1 °C | 70.61 mm |
| Annual | 7.2 °C | 19.3 °C | 1131.57 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 11 - Apr. 20 |
| Average Days With Frost | 100-125 Days |
| Plant Hardiness Zone | Zone 6b : -20.6°C to -17.8°C |
| Plant Hardiness Zone - 2012 | Zone 6a : -23.3°C to -20.6°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |