Leland, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 4.1 °C (low) to 15.1 °C (high). Annual precipitation averages 961.6 Millimeters. Leland 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 | -10.1 °C | -1.3 °C | 45.21 mm |
| February | -8.1 °C | 1.2 °C | 44.7 mm |
| March | -2.6 °C | 8.1 °C | 58.93 mm |
| April | 3.2 °C | 15.6 °C | 92.2 mm |
| May | 9.7 °C | 21.9 °C | 120.4 mm |
| June | 15.2 °C | 26.9 °C | 117.6 mm |
| July | 17.1 °C | 28.6 °C | 102.11 mm |
| August | 15.9 °C | 27.5 °C | 98.04 mm |
| September | 11.4 °C | 24.5 °C | 87.88 mm |
| October | 4.9 °C | 17.4 °C | 79.76 mm |
| November | -1 °C | 9 °C | 63.5 mm |
| December | -6.7 °C | 1.8 °C | 51.31 mm |
| Annual | 4.1 °C | 15.1 °C | 961.64 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 |