Marengo, Iowa has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 39.1 °F (low) to 59.5 °F (high). Annual precipitation averages 37 Inches. 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 | 12.1 °F | 29.0 °F | 1.14 in. |
| February | 15.8 °F | 33.8 °F | 1.33 in. |
| March | 27.0 °F | 46.9 °F | 2.14 in. |
| April | 38.0 °F | 60.9 °F | 3.68 in. |
| May | 50.3 °F | 72.0 °F | 4.77 in. |
| June | 60.6 °F | 81.3 °F | 5.2 in. |
| July | 64.0 °F | 84.7 °F | 4.26 in. |
| August | 61.4 °F | 82.9 °F | 4.3 in. |
| September | 52.6 °F | 76.7 °F | 3.58 in. |
| October | 40.5 °F | 63.6 °F | 2.85 in. |
| November | 28.6 °F | 47.8 °F | 2.12 in. |
| December | 18.2 °F | 34.5 °F | 1.6 in. |
| Annual | 39.1 °F | 59.5 °F | 36.97 in. |
| 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 : -15°F to -10°F |
| Plant Hardiness Zone - 2012 | Zone 5a : -20°F to -15°F |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |