Norwalk, Iowa has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 4.6 °C (low) to 15.8 °C (high). Annual precipitation averages 907.1 Millimeters. Norwalk is located in USDA Plant Hardiness Zone 5b. The growing season typically runs from the last frost around Apr. 11 - Apr. 20 through the first frost around Oct. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -10.4 °C | -0.7 °C | 25.91 mm |
| February | -8.3 °C | 1.9 °C | 31.75 mm |
| March | -2.2 °C | 9.1 °C | 51.82 mm |
| April | 4.1 °C | 16.4 °C | 93.22 mm |
| May | 10.7 °C | 22.2 °C | 131.06 mm |
| June | 16.4 °C | 27.5 °C | 130.05 mm |
| July | 18.6 °C | 29.7 °C | 104.39 mm |
| August | 17.2 °C | 28.8 °C | 104.14 mm |
| September | 12.3 °C | 25.1 °C | 87.38 mm |
| October | 5.4 °C | 17.8 °C | 65.28 mm |
| November | -1.3 °C | 9.3 °C | 45.47 mm |
| December | -7.3 °C | 2.2 °C | 36.58 mm |
| Annual | 4.6 °C | 15.8 °C | 907.05 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 11 - Apr. 20 |
| Average Days With Frost | 125-150 Days |
| Plant Hardiness Zone | Zone 5b : -26.1°C to -23.3°C |
| Plant Hardiness Zone - 2012 | Zone 5b : -26.1°C to -23.3°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |