Westville, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 5.7 °C (low) to 16.8 °C (high). Annual precipitation averages 1045 Millimeters. Westville is located in USDA Plant Hardiness Zone 6a. The growing season typically runs from the last frost around Apr. 11 - Apr. 20 through the first frost around Oct. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -7.7 °C | 1.2 °C | 62.74 mm |
| February | -5.9 °C | 3.7 °C | 54.86 mm |
| March | -0.7 °C | 10.2 °C | 74.93 mm |
| April | 5.1 °C | 17.5 °C | 106.68 mm |
| May | 11.4 °C | 23.4 °C | 117.09 mm |
| June | 16.6 °C | 28 °C | 124.71 mm |
| July | 17.9 °C | 29.4 °C | 107.19 mm |
| August | 16.7 °C | 28.7 °C | 82.55 mm |
| September | 12.5 °C | 26 °C | 76.45 mm |
| October | 6.2 °C | 19.1 °C | 87.38 mm |
| November | 0.4 °C | 10.7 °C | 85.6 mm |
| December | -4.5 °C | 3.9 °C | 64.77 mm |
| Annual | 5.7 °C | 16.8 °C | 1044.95 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 11 - Apr. 20 |
| Average Days With Frost | 100-125 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 |