Thebes, Illinois has a Humid Subtropical Climate climate (Köppen classification: Cfa). Average annual temperatures range from 8.6 °C (low) to 20 °C (high). Annual precipitation averages 1260.9 Millimeters. Thebes 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 | -3.4 °C | 5.9 °C | 90.93 mm |
| February | -1.7 °C | 8.9 °C | 91.19 mm |
| March | 2.8 °C | 14.3 °C | 118.11 mm |
| April | 8.3 °C | 20.5 °C | 140.72 mm |
| May | 14.1 °C | 25.4 °C | 138.68 mm |
| June | 18.7 °C | 30.2 °C | 107.19 mm |
| July | 20.7 °C | 31.8 °C | 95.76 mm |
| August | 19.3 °C | 31.2 °C | 78.23 mm |
| September | 14.8 °C | 27.9 °C | 85.34 mm |
| October | 8.3 °C | 21.9 °C | 97.54 mm |
| November | 2.7 °C | 14.1 °C | 118.87 mm |
| December | -1.4 °C | 7.9 °C | 98.3 mm |
| Annual | 8.6 °C | 20 °C | 1260.86 mm |
| 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 : -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 | Cfa - Humid Subtropical Climate |