Shirley, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 5.1 °C (low) to 16.5 °C (high). Annual precipitation averages 994.4 Millimeters. Shirley is located in USDA Plant Hardiness Zone 6a. 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 | -8.7 °C | 0.4 °C | 58.17 mm |
| February | -6.8 °C | 3.2 °C | 49.78 mm |
| March | -1.6 °C | 9.8 °C | 68.58 mm |
| April | 4.4 °C | 17.2 °C | 97.54 mm |
| May | 10.8 °C | 23.2 °C | 114.81 mm |
| June | 16.2 °C | 28.1 °C | 109.73 mm |
| July | 17.9 °C | 29.8 °C | 99.82 mm |
| August | 16.8 °C | 28.7 °C | 94.23 mm |
| September | 12.4 °C | 25.9 °C | 84.84 mm |
| October | 6 °C | 18.6 °C | 85.6 mm |
| November | -0.2 °C | 10.3 °C | 71.37 mm |
| December | -5.5 °C | 3.3 °C | 59.94 mm |
| Annual | 5.1 °C | 16.5 °C | 994.41 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 6a : -23.3°C to -20.6°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 |