Granite City, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 8.4 °C (low) to 19.1 °C (high). Annual precipitation averages 1128 Millimeters. Granite City 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 | -4.8 °C | 4.4 °C | 67.06 mm |
| February | -2.8 °C | 7.4 °C | 61.47 mm |
| March | 2 °C | 12.9 °C | 87.63 mm |
| April | 8 °C | 19.7 °C | 121.41 mm |
| May | 13.8 °C | 24.8 °C | 135.89 mm |
| June | 18.8 °C | 29.6 °C | 116.59 mm |
| July | 20.9 °C | 31.5 °C | 106.17 mm |
| August | 19.9 °C | 30.8 °C | 101.35 mm |
| September | 15.2 °C | 27.1 °C | 84.58 mm |
| October | 8.8 °C | 20.8 °C | 82.8 mm |
| November | 2.7 °C | 13.1 °C | 92.71 mm |
| December | -2.3 °C | 6.9 °C | 70.36 mm |
| Annual | 8.4 °C | 19.1 °C | 1128.02 mm |
| Average First Frost Date | Nov. 1 - Nov. 10 |
| Average Last Frost Date | Mar. 21 - Mar. 31 |
| 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 |