Granite City, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 47 °F (low) to 66.3 °F (high). Annual precipitation averages 44.4 Inches. 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 | 23.3 °F | 39.9 °F | 2.64 in. |
| February | 26.9 °F | 45.3 °F | 2.42 in. |
| March | 35.6 °F | 55.2 °F | 3.45 in. |
| April | 46.4 °F | 67.4 °F | 4.78 in. |
| May | 56.9 °F | 76.6 °F | 5.35 in. |
| June | 65.9 °F | 85.3 °F | 4.59 in. |
| July | 69.7 °F | 88.7 °F | 4.18 in. |
| August | 67.9 °F | 87.4 °F | 3.99 in. |
| September | 59.4 °F | 80.8 °F | 3.33 in. |
| October | 47.8 °F | 69.4 °F | 3.26 in. |
| November | 36.8 °F | 55.6 °F | 3.65 in. |
| December | 27.9 °F | 44.4 °F | 2.77 in. |
| Annual | 47 °F | 66.3 °F | 44.41 in. |
| 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 : 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 |