Glen Carbon, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 47 °F (low) to 65.9 °F (high). Annual precipitation averages 44.7 Inches. Glen Carbon is located in USDA Plant Hardiness Zone 7a. The growing season typically runs from the last frost around Apr. 1 - Apr. 10 through the first frost around Oct. 21 - Oct. 31.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 23.3 °F | 39.6 °F | 2.67 in. |
| February | 26.7 °F | 45.0 °F | 2.43 in. |
| March | 35.4 °F | 55.1 °F | 3.5 in. |
| April | 46.3 °F | 66.9 °F | 4.94 in. |
| May | 57.0 °F | 76.0 °F | 5.25 in. |
| June | 65.9 °F | 84.8 °F | 4.79 in. |
| July | 69.7 °F | 87.9 °F | 4.39 in. |
| August | 67.7 °F | 86.9 °F | 3.94 in. |
| September | 59.4 °F | 80.6 °F | 3.17 in. |
| October | 47.8 °F | 69.0 °F | 3.31 in. |
| November | 36.6 °F | 55.1 °F | 3.59 in. |
| December | 27.9 °F | 44.1 °F | 2.73 in. |
| Annual | 47 °F | 65.9 °F | 44.71 in. |
| Average First Frost Date | Oct. 21 - Oct. 31 |
| Average Last Frost Date | Apr. 1 - Apr. 10 |
| Average Days With Frost | 75-100 Days |
| Plant Hardiness Zone | Zone 7a : 0°F to 5°F |
| Plant Hardiness Zone - 2012 | Zone 6b : -5°F to 0°F |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |