DeWitt, Iowa has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 4.2 °C (low) to 15.1 °C (high). Annual precipitation averages 965 Millimeters. DeWitt 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 | -10.7 °C | -1.5 °C | 34.54 mm |
| February | -8.6 °C | 1 °C | 41.91 mm |
| March | -2.6 °C | 8.2 °C | 61.21 mm |
| April | 3.6 °C | 15.7 °C | 95.76 mm |
| May | 10.2 °C | 21.9 °C | 119.89 mm |
| June | 15.8 °C | 27.1 °C | 121.92 mm |
| July | 17.7 °C | 28.7 °C | 109.47 mm |
| August | 16.4 °C | 27.7 °C | 110.74 mm |
| September | 11.8 °C | 24.5 °C | 93.73 mm |
| October | 5.3 °C | 17.3 °C | 73.41 mm |
| November | -1.3 °C | 8.9 °C | 55.63 mm |
| December | -7.1 °C | 1.6 °C | 46.74 mm |
| Annual | 4.2 °C | 15.1 °C | 964.95 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 11 - Apr. 20 |
| Average Days With Frost | 100-125 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 | Abnormally Dry |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |