Vergennes, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 46.2 °F (low) to 66.6 °F (high). Annual precipitation averages 46.6 Inches. Vergennes is located in USDA Plant Hardiness Zone 7a. The growing season typically runs from the last frost around Apr. 1 - Apr. 10 through the first frost around Oct. 21 - Oct. 31.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 23.9 °F | 40.8 °F | 3.1 in. |
| February | 27.4 °F | 45.7 °F | 2.91 in. |
| March | 35.6 °F | 55.9 °F | 4.13 in. |
| April | 45.8 °F | 67.4 °F | 5.21 in. |
| May | 56.2 °F | 76.5 °F | 5.32 in. |
| June | 64.9 °F | 85.3 °F | 4.68 in. |
| July | 68.3 °F | 88.0 °F | 3.95 in. |
| August | 65.7 °F | 86.9 °F | 3.11 in. |
| September | 57.3 °F | 81.1 °F | 3.22 in. |
| October | 45.7 °F | 70.0 °F | 3.52 in. |
| November | 35.8 °F | 56.2 °F | 4.09 in. |
| December | 28.0 °F | 45.0 °F | 3.33 in. |
| Annual | 46.2 °F | 66.6 °F | 46.57 in. |
| Average First Frost Date | Oct. 21 - Oct. 31 |
| Average Last Frost Date | Apr. 1 - Apr. 10 |
| Average Days With Frost | 75-100 Days |
| Plant Hardiness Zone | Zone 7a : 0°F to 5°F |
| Plant Hardiness Zone - 2012 | Zone 6b : -5°F to 0°F |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |