Lebanon, Illinois has a Humid Subtropical Climate climate (Köppen classification: Cfa). Average annual temperatures range from 7.9 °C (low) to 18.9 °C (high). Annual precipitation averages 1143.3 Millimeters. Lebanon is located in USDA Plant Hardiness Zone 6b. The growing season typically runs from the last frost around Apr. 1 - Apr. 10 through the first frost around Oct. 21 - Oct. 31.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -5.2 °C | 4.2 °C | 74.42 mm |
| February | -3.3 °C | 7.2 °C | 62.74 mm |
| March | 1.6 °C | 12.9 °C | 89.66 mm |
| April | 7.6 °C | 19.5 °C | 131.06 mm |
| May | 13.6 °C | 24.5 °C | 134.37 mm |
| June | 18.5 °C | 29.5 °C | 126.49 mm |
| July | 20.6 °C | 31.3 °C | 99.82 mm |
| August | 19.4 °C | 30.7 °C | 84.33 mm |
| September | 14.7 °C | 27.2 °C | 88.14 mm |
| October | 8.2 °C | 20.8 °C | 81.28 mm |
| November | 2.1 °C | 12.8 °C | 98.55 mm |
| December | -2.7 °C | 6.7 °C | 72.39 mm |
| Annual | 7.9 °C | 18.9 °C | 1143.25 mm |
| Average First Frost Date | Oct. 21 - Oct. 31 |
| Average Last Frost Date | Apr. 1 - Apr. 10 |
| Average Days With Frost | 75-100 Days |
| Plant Hardiness Zone | Zone 6b : -20.6°C to -17.8°C |
| Plant Hardiness Zone - 2012 | Zone 6b : -20.6°C to -17.8°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Cfa - Humid Subtropical Climate |