Karnak, Illinois has a Humid Subtropical Climate climate (Köppen classification: Cfa). Average annual temperatures range from 8.8 °C (low) to 19.8 °C (high). Annual precipitation averages 1264.7 Millimeters. Karnak is located in USDA Plant Hardiness Zone 7a. The growing season typically runs from the last frost around Mar. 21 - Mar. 31 through the first frost around Nov. 1 - Nov. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -3.1 °C | 6.1 °C | 97.28 mm |
| February | -1.4 °C | 8.7 °C | 90.17 mm |
| March | 2.9 °C | 14.1 °C | 119.38 mm |
| April | 8.5 °C | 20.2 °C | 133.6 mm |
| May | 14.1 °C | 25 °C | 133.86 mm |
| June | 18.7 °C | 29.7 °C | 114.81 mm |
| July | 20.7 °C | 31.4 °C | 100.58 mm |
| August | 19.5 °C | 30.8 °C | 72.14 mm |
| September | 15.2 °C | 27.7 °C | 87.12 mm |
| October | 8.7 °C | 21.7 °C | 97.79 mm |
| November | 3 °C | 14.1 °C | 108.71 mm |
| December | -1 °C | 8 °C | 109.22 mm |
| Annual | 8.8 °C | 19.8 °C | 1264.66 mm |
| Average First Frost Date | Nov. 1 - Nov. 10 |
| Average Last Frost Date | Mar. 21 - Mar. 31 |
| Average Days With Frost | 50-75 Days |
| Plant Hardiness Zone | Zone 7a : -17.8°C to -15°C |
| Plant Hardiness Zone - 2012 | Zone 7a : -17.8°C to -15°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Cfa - Humid Subtropical Climate |