McLeansboro, Illinois has a Humid Subtropical Climate climate (Köppen classification: Cfa). Average annual temperatures range from 7.5 °C (low) to 18.9 °C (high). Annual precipitation averages 1170.9 Millimeters. McLeansboro is located in USDA Plant Hardiness Zone 6b. 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 | -4.8 °C | 4.4 °C | 92.46 mm |
| February | -3.3 °C | 7.2 °C | 71.88 mm |
| March | 1.6 °C | 12.8 °C | 106.17 mm |
| April | 7.2 °C | 19.3 °C | 128.27 mm |
| May | 12.9 °C | 24.4 °C | 132.08 mm |
| June | 17.9 °C | 29.1 °C | 113.28 mm |
| July | 19.6 °C | 31.1 °C | 95.76 mm |
| August | 18.4 °C | 30.7 °C | 72.39 mm |
| September | 13.9 °C | 27.3 °C | 77.72 mm |
| October | 7.5 °C | 20.8 °C | 86.11 mm |
| November | 1.7 °C | 13 °C | 105.92 mm |
| December | -2.7 °C | 6.8 °C | 88.9 mm |
| Annual | 7.5 °C | 18.9 °C | 1170.94 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 11 - Apr. 20 |
| Average Days With Frost | 75-100 Days |
| Plant Hardiness Zone | Zone 6b : -20.6°C to -17.8°C |
| Plant Hardiness Zone - 2012 | Zone 6a : -23.3°C to -20.6°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Cfa - Humid Subtropical Climate |