Onawa, Iowa has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 3.3 °C (low) to 16.1 °C (high). Annual precipitation averages 801.1 Millimeters. Onawa 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 | -11.7 °C | -0.8 °C | 17.02 mm |
| February | -9.5 °C | 1.9 °C | 21.34 mm |
| March | -3.4 °C | 9.4 °C | 41.66 mm |
| April | 2.7 °C | 16.9 °C | 89.66 mm |
| May | 9.6 °C | 22.9 °C | 116.84 mm |
| June | 15.6 °C | 28.3 °C | 116.59 mm |
| July | 17.7 °C | 30.1 °C | 96.52 mm |
| August | 16.2 °C | 28.8 °C | 102.62 mm |
| September | 11.1 °C | 25.6 °C | 78.49 mm |
| October | 3.9 °C | 18.5 °C | 57.15 mm |
| November | -3.3 °C | 9.3 °C | 35.05 mm |
| December | -9 °C | 1.7 °C | 28.19 mm |
| Annual | 3.3 °C | 16.1 °C | 801.13 mm |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | Apr. 21 - Apr. 30 |
| Average Days With Frost | 150-180 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 | Abnormally Dry |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |