Charleston, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 43.8 °F (low) to 63.5 °F (high). Annual precipitation averages 42.6 Inches. Charleston is located in USDA Plant Hardiness Zone 6a. 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 | 20.2 °F | 35.9 °F | 2.74 in. |
| February | 23.2 °F | 40.5 °F | 2.33 in. |
| March | 32.2 °F | 51.8 °F | 3.03 in. |
| April | 43.0 °F | 64.7 °F | 4.87 in. |
| May | 54.2 °F | 74.7 °F | 4.44 in. |
| June | 63.0 °F | 83.1 °F | 4.86 in. |
| July | 65.8 °F | 86.3 °F | 4.22 in. |
| August | 63.8 °F | 85.0 °F | 2.85 in. |
| September | 56.0 °F | 79.6 °F | 3.06 in. |
| October | 44.7 °F | 67.2 °F | 3.62 in. |
| November | 34.1 °F | 52.7 °F | 3.73 in. |
| December | 25.6 °F | 40.7 °F | 2.85 in. |
| Annual | 43.8 °F | 63.5 °F | 42.6 in. |
| 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 6a : -10°F to -5°F |
| Plant Hardiness Zone - 2012 | Zone 6a : -10°F to -5°F |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |