De Witt, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 5.4 °C (low) to 16.7 °C (high). Annual precipitation averages 1000 Millimeters. De Witt is located in USDA Plant Hardiness Zone 6a. 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 | -8.2 °C | 0.9 °C | 57.15 mm |
| February | -6.4 °C | 3.4 °C | 50.29 mm |
| March | -1.4 °C | 9.9 °C | 68.33 mm |
| April | 4.7 °C | 17.5 °C | 99.06 mm |
| May | 11.2 °C | 23.3 °C | 113.03 mm |
| June | 16.3 °C | 28.1 °C | 114.05 mm |
| July | 18.1 °C | 29.6 °C | 105.41 mm |
| August | 16.8 °C | 28.8 °C | 87.38 mm |
| September | 12.6 °C | 26 °C | 83.57 mm |
| October | 5.9 °C | 18.8 °C | 86.11 mm |
| November | -0.1 °C | 10.5 °C | 74.42 mm |
| December | -5 °C | 3.6 °C | 61.21 mm |
| Annual | 5.4 °C | 16.7 °C | 1000.01 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 6a : -23.3°C to -20.6°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 |