Mount Union, Iowa has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 5.1 °C (low) to 16.1 °C (high). Annual precipitation averages 963.9 Millimeters. Mount Union is located in USDA Plant Hardiness Zone 5b. The growing season typically runs from the last frost around Apr. 21 - Apr. 30 through the first frost around Oct. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -9.3 °C | -0.2 °C | 37.08 mm |
| February | -7.2 °C | 2.5 °C | 44.45 mm |
| March | -1.6 °C | 9.6 °C | 61.98 mm |
| April | 4.6 °C | 16.8 °C | 94.49 mm |
| May | 11.2 °C | 22.7 °C | 129.54 mm |
| June | 16.6 °C | 27.8 °C | 124.46 mm |
| July | 18.4 °C | 29.6 °C | 103.12 mm |
| August | 17.2 °C | 28.8 °C | 100.58 mm |
| September | 12.3 °C | 25.3 °C | 91.44 mm |
| October | 5.9 °C | 18.2 °C | 73.15 mm |
| November | -0.4 °C | 9.7 °C | 57.91 mm |
| December | -6 °C | 2.8 °C | 45.72 mm |
| Annual | 5.1 °C | 16.1 °C | 963.92 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 21 - Apr. 30 |
| 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 |