Grand Tower, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 8.2 °C (low) to 19.7 °C (high). Annual precipitation averages 1164.1 Millimeters. Grand Tower 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 | -4.3 °C | 5.3 °C | 75.44 mm |
| February | -2.1 °C | 8.2 °C | 76.96 mm |
| March | 2.1 °C | 13.8 °C | 109.47 mm |
| April | 7.9 °C | 20.1 °C | 132.84 mm |
| May | 13.7 °C | 25.1 °C | 130.81 mm |
| June | 18.7 °C | 30.1 °C | 114.81 mm |
| July | 20.6 °C | 31.8 °C | 90.17 mm |
| August | 19.1 °C | 31 °C | 75.18 mm |
| September | 14.4 °C | 28.1 °C | 75.95 mm |
| October | 7.7 °C | 21.7 °C | 86.11 mm |
| November | 2.5 °C | 13.8 °C | 109.98 mm |
| December | -2.1 °C | 7.5 °C | 86.36 mm |
| Annual | 8.2 °C | 19.7 °C | 1164.08 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 | Dfa - Humid Continental Hot Summers With Year Around Precipitation |