Rock City, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 3.3 °C (low) to 14.1 °C (high). Annual precipitation averages 953 Millimeters. Rock City is located in USDA Plant Hardiness Zone 5a. The growing season typically runs from the last frost around Apr. 21 - Apr. 30 through the first frost around Oct. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -11.3 °C | -2.3 °C | 39.37 mm |
| February | -9.4 °C | -0.1 °C | 41.4 mm |
| March | -3.6 °C | 6.8 °C | 53.34 mm |
| April | 2.4 °C | 14.4 °C | 94.23 mm |
| May | 8.9 °C | 20.8 °C | 107.95 mm |
| June | 14.6 °C | 26.2 °C | 136.14 mm |
| July | 16.5 °C | 27.9 °C | 103.12 mm |
| August | 15.4 °C | 27 °C | 100.58 mm |
| September | 10.8 °C | 23.3 °C | 96.77 mm |
| October | 4.4 °C | 16.2 °C | 74.68 mm |
| November | -1.8 °C | 7.8 °C | 57.91 mm |
| December | -7.6 °C | 0.7 °C | 47.5 mm |
| Annual | 3.3 °C | 14.1 °C | 952.99 mm |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | Apr. 21 - Apr. 30 |
| Average Days With Frost | 125-150 Days |
| Plant Hardiness Zone | Zone 5a : -28.9°C to -26.1°C |
| Plant Hardiness Zone - 2012 | Zone 5a : -28.9°C to -26.1°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |