Unionville, Iowa has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 4.6 °C (low) to 15.9 °C (high). Annual precipitation averages 980.7 Millimeters. Unionville is located in USDA Plant Hardiness Zone 5b. 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 | -10.2 °C | -0.2 °C | 30.48 mm |
| February | -8 °C | 2.4 °C | 39.12 mm |
| March | -2.1 °C | 9.7 °C | 56.9 mm |
| April | 4.1 °C | 16.6 °C | 99.31 mm |
| May | 10.6 °C | 21.9 °C | 136.4 mm |
| June | 16.1 °C | 27.2 °C | 136.14 mm |
| July | 18.2 °C | 29.4 °C | 112.78 mm |
| August | 16.9 °C | 28.7 °C | 105.66 mm |
| September | 12.1 °C | 24.8 °C | 96.77 mm |
| October | 5.4 °C | 17.8 °C | 73.66 mm |
| November | -1.4 °C | 9.6 °C | 54.61 mm |
| December | -6.8 °C | 2.7 °C | 38.86 mm |
| Annual | 4.6 °C | 15.9 °C | 980.69 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 5b : -26.1°C to -23.3°C |
| Plant Hardiness Zone - 2012 | Zone 5b : -26.1°C to -23.3°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |