Unionville, Michigan has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 3.5 °C (low) to 13.4 °C (high). Annual precipitation averages 787.7 Millimeters. Unionville is located in USDA Plant Hardiness Zone 6a. The growing season typically runs from the last frost around May 1 - May 10 through the first frost around Oct. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -9.1 °C | -1.7 °C | 42.93 mm |
| February | -9 °C | -0.2 °C | 39.12 mm |
| March | -4.4 °C | 5.1 °C | 40.89 mm |
| April | 1.7 °C | 12.6 °C | 82.3 mm |
| May | 8.1 °C | 19.6 °C | 83.57 mm |
| June | 13.6 °C | 24.9 °C | 86.36 mm |
| July | 15.6 °C | 27.2 °C | 78.74 mm |
| August | 14.7 °C | 26 °C | 82.04 mm |
| September | 10.8 °C | 22.7 °C | 73.41 mm |
| October | 5 °C | 15.4 °C | 74.42 mm |
| November | -0.3 °C | 7.7 °C | 58.67 mm |
| December | -5.1 °C | 1.4 °C | 45.21 mm |
| Annual | 3.5 °C | 13.4 °C | 787.66 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | 125-150 Days |
| Plant Hardiness Zone | Zone 6a : -23.3°C to -20.6°C |
| Plant Hardiness Zone - 2012 | Zone 6a : -23.3°C to -20.6°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |