Symerton, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 5 °C (low) to 15.6 °C (high). Annual precipitation averages 1001.8 Millimeters. Symerton is located in USDA Plant Hardiness Zone 5b. 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 | -8.8 °C | -0.3 °C | 54.61 mm |
| February | -7.1 °C | 2.1 °C | 50.29 mm |
| March | -1.8 °C | 8.6 °C | 60.45 mm |
| April | 3.9 °C | 15.9 °C | 96.77 mm |
| May | 10.2 °C | 21.9 °C | 118.11 mm |
| June | 15.7 °C | 27.2 °C | 118.36 mm |
| July | 17.9 °C | 28.9 °C | 112.27 mm |
| August | 17 °C | 28.1 °C | 101.85 mm |
| September | 12.4 °C | 25 °C | 85.85 mm |
| October | 5.8 °C | 17.8 °C | 83.31 mm |
| November | 0.1 °C | 9.6 °C | 64.77 mm |
| December | -5.6 °C | 2.7 °C | 55.12 mm |
| Annual | 5 °C | 15.6 °C | 1001.76 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 11 - Apr. 20 |
| Average Days With Frost | 100-125 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 |