Williamsville, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 42.7 °F (low) to 63 °F (high). Annual precipitation averages 38.7 Inches. Williamsville 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 | 18.5 °F | 35.0 °F | 2.1 in. |
| February | 21.6 °F | 39.8 °F | 1.93 in. |
| March | 30.9 °F | 51.5 °F | 2.67 in. |
| April | 41.8 °F | 64.3 °F | 4.05 in. |
| May | 53.3 °F | 74.2 °F | 4.53 in. |
| June | 62.4 °F | 82.8 °F | 4.53 in. |
| July | 65.4 °F | 85.8 °F | 3.8 in. |
| August | 63.5 °F | 84.3 °F | 3.45 in. |
| September | 55.0 °F | 79.1 °F | 3.24 in. |
| October | 43.4 °F | 66.6 °F | 3.29 in. |
| November | 32.6 °F | 52.0 °F | 2.93 in. |
| December | 23.9 °F | 40.0 °F | 2.19 in. |
| Annual | 42.7 °F | 63 °F | 38.71 in. |
| 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 : -10°F to -5°F |
| Plant Hardiness Zone - 2012 | Zone 5b : -15°F to -10°F |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |