Marengo, Iowa has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 3.9 °C (low) to 15.3 °C (high). Annual precipitation averages 939 Millimeters. Marengo 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. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -11.1 °C | -1.7 °C | 28.96 mm |
| February | -9 °C | 1 °C | 33.78 mm |
| March | -2.8 °C | 8.3 °C | 54.36 mm |
| April | 3.3 °C | 16.1 °C | 93.47 mm |
| May | 10.2 °C | 22.2 °C | 121.16 mm |
| June | 15.9 °C | 27.4 °C | 132.08 mm |
| July | 17.8 °C | 29.3 °C | 108.2 mm |
| August | 16.3 °C | 28.3 °C | 109.22 mm |
| September | 11.4 °C | 24.8 °C | 90.93 mm |
| October | 4.7 °C | 17.6 °C | 72.39 mm |
| November | -1.9 °C | 8.8 °C | 53.85 mm |
| December | -7.7 °C | 1.4 °C | 40.64 mm |
| Annual | 3.9 °C | 15.3 °C | 939.04 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 5b : -26.1°C to -23.3°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 |