Walnut, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 4.2 °C (low) to 15.2 °C (high). Annual precipitation averages 952.5 Millimeters. Walnut 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. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -10.2 °C | -1.2 °C | 43.94 mm |
| February | -8.1 °C | 1.4 °C | 42.42 mm |
| March | -2.6 °C | 8.3 °C | 58.93 mm |
| April | 3.4 °C | 15.8 °C | 88.39 mm |
| May | 10.1 °C | 22.1 °C | 121.67 mm |
| June | 15.5 °C | 27 °C | 128.27 mm |
| July | 17.3 °C | 28.7 °C | 100.08 mm |
| August | 16.1 °C | 27.7 °C | 101.6 mm |
| September | 11.5 °C | 24.6 °C | 84.07 mm |
| October | 5.1 °C | 17.6 °C | 77.22 mm |
| November | -1.2 °C | 9 °C | 59.18 mm |
| December | -6.8 °C | 1.9 °C | 46.74 mm |
| Annual | 4.2 °C | 15.2 °C | 952.51 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 21 - Apr. 30 |
| 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 |