Winnebago, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 3.4 °C (low) to 14.2 °C (high). Annual precipitation averages 957.3 Millimeters. Winnebago 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 | -11.1 °C | -2.2 °C | 40.64 mm |
| February | -9.2 °C | 0.1 °C | 42.16 mm |
| March | -3.4 °C | 6.9 °C | 54.86 mm |
| April | 2.5 °C | 14.5 °C | 94.23 mm |
| May | 9.1 °C | 20.9 °C | 113.79 mm |
| June | 14.7 °C | 26.1 °C | 135.89 mm |
| July | 16.6 °C | 27.8 °C | 104.39 mm |
| August | 15.6 °C | 27 °C | 104.9 mm |
| September | 10.8 °C | 23.6 °C | 88.14 mm |
| October | 4.4 °C | 16.4 °C | 73.41 mm |
| November | -1.7 °C | 7.9 °C | 55.63 mm |
| December | -7.4 °C | 0.9 °C | 49.28 mm |
| Annual | 3.4 °C | 14.2 °C | 957.32 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 5a : -28.9°C to -26.1°C |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |