Harpers Ferry, Iowa has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 3.2 °C (low) to 14.3 °C (high). Annual precipitation averages 935.7 Millimeters. Harpers Ferry is located in USDA Plant Hardiness Zone 5a. 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 | -12 °C | -2.6 °C | 32.51 mm |
| February | -10.1 °C | 0 °C | 30.23 mm |
| March | -3.7 °C | 6.8 °C | 50.8 mm |
| April | 2.6 °C | 14.9 °C | 96.77 mm |
| May | 9 °C | 21.4 °C | 120.4 mm |
| June | 14.6 °C | 26.7 °C | 139.95 mm |
| July | 17 °C | 28.7 °C | 112.27 mm |
| August | 15.8 °C | 27.6 °C | 100.08 mm |
| September | 11.2 °C | 23.7 °C | 96.52 mm |
| October | 4.5 °C | 16.3 °C | 66.29 mm |
| November | -2.2 °C | 7.6 °C | 51.82 mm |
| December | -7.9 °C | 0.4 °C | 38.1 mm |
| Annual | 3.2 °C | 14.3 °C | 935.74 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 21 - Apr. 30 |
| Average Days With Frost | 125-150 Days |
| Plant Hardiness Zone | Zone 5a : -28.9°C to -26.1°C |
| Plant Hardiness Zone - 2012 | Zone 5a : -28.9°C to -26.1°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |