Big Rock, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 4.1 °C (low) to 15 °C (high). Annual precipitation averages 960.1 Millimeters. Big Rock is located in USDA Plant Hardiness Zone 5b. The growing season typically runs from the last frost around Apr. 21 - Apr. 30 through the first frost around Oct. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -9.9 °C | -1.2 °C | 47.5 mm |
| February | -8.2 °C | 1.1 °C | 46.74 mm |
| March | -2.7 °C | 7.9 °C | 59.18 mm |
| April | 3.2 °C | 15.2 °C | 94.74 mm |
| May | 9.6 °C | 21.5 °C | 121.41 mm |
| June | 15.1 °C | 26.9 °C | 112.27 mm |
| July | 17.2 °C | 28.7 °C | 96.01 mm |
| August | 16 °C | 27.6 °C | 97.03 mm |
| September | 11.5 °C | 24.3 °C | 84.33 mm |
| October | 4.9 °C | 17.2 °C | 83.31 mm |
| November | -1 °C | 8.9 °C | 63.5 mm |
| December | -6.6 °C | 1.8 °C | 54.1 mm |
| Annual | 4.1 °C | 15 °C | 960.12 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 21 - Apr. 30 |
| Average Days With Frost | 125-150 Days |
| Plant Hardiness Zone | Zone 5b : -26.1°C to -23.3°C |
| Plant Hardiness Zone - 2012 | Zone 5b : -26.1°C to -23.3°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |