Garnavillo, Iowa has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 2.6 °C (low) to 13.5 °C (high). Annual precipitation averages 966.7 Millimeters. Garnavillo 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. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -12.9 °C | -3.6 °C | 31.5 mm |
| February | -11 °C | -0.9 °C | 31.24 mm |
| March | -4.3 °C | 6.1 °C | 51.31 mm |
| April | 2.1 °C | 14 °C | 98.3 mm |
| May | 8.6 °C | 20.6 °C | 120.14 mm |
| June | 14.4 °C | 25.8 °C | 149.1 mm |
| July | 16.6 °C | 27.7 °C | 119.89 mm |
| August | 15.3 °C | 26.6 °C | 101.6 mm |
| September | 10.6 °C | 22.9 °C | 96.77 mm |
| October | 3.8 °C | 15.8 °C | 72.64 mm |
| November | -2.9 °C | 6.8 °C | 53.59 mm |
| December | -8.9 °C | -0.4 °C | 40.64 mm |
| Annual | 2.6 °C | 13.5 °C | 966.72 mm |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| 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 |