Sumner, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 7.2 °C (low) to 18.6 °C (high). Annual precipitation averages 1199.1 Millimeters. Sumner 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. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -5.3 °C | 3.7 °C | 87.12 mm |
| February | -3.6 °C | 6.5 °C | 67.06 mm |
| March | 1 °C | 12.3 °C | 97.54 mm |
| April | 6.8 °C | 19.1 °C | 128.27 mm |
| May | 12.9 °C | 24.5 °C | 132.33 mm |
| June | 17.8 °C | 29.3 °C | 125.73 mm |
| July | 19.2 °C | 30.8 °C | 112.78 mm |
| August | 17.9 °C | 30.3 °C | 78.23 mm |
| September | 13.6 °C | 27.4 °C | 88.14 mm |
| October | 7.2 °C | 20.7 °C | 93.73 mm |
| November | 1.5 °C | 12.7 °C | 101.6 mm |
| December | -2.9 °C | 6.2 °C | 86.61 mm |
| Annual | 7.2 °C | 18.6 °C | 1199.14 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 1 - Apr. 10 |
| Average Days With Frost | 100-125 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 | Dfa - Humid Continental Hot Summers With Year Around Precipitation |