Chester, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 7.6 °C (low) to 19.2 °C (high). Annual precipitation averages 1115.6 Millimeters. Chester is located in USDA Plant Hardiness Zone 7a. 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 | 5.1 °C | 70.87 mm |
| February | -2.9 °C | 8 °C | 66.8 mm |
| March | 1.6 °C | 13.5 °C | 90.93 mm |
| April | 7.2 °C | 19.8 °C | 125.73 mm |
| May | 12.9 °C | 24.6 °C | 136.4 mm |
| June | 17.8 °C | 29.3 °C | 108.71 mm |
| July | 19.9 °C | 31.1 °C | 100.58 mm |
| August | 18.7 °C | 30.7 °C | 76.71 mm |
| September | 14.1 °C | 27.1 °C | 80.26 mm |
| October | 7.7 °C | 21 °C | 81.53 mm |
| November | 2 °C | 13.3 °C | 99.06 mm |
| December | -2.7 °C | 7.2 °C | 77.98 mm |
| Annual | 7.6 °C | 19.2 °C | 1115.56 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 7a : -17.8°C to -15°C |
| Plant Hardiness Zone - 2012 | Zone 6b : -20.6°C to -17.8°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |