Winnetka, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 6.4 °C (low) to 14.6 °C (high). Annual precipitation averages 985.3 Millimeters. Winnetka 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. 21 - Oct. 31.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -7.3 °C | -0.1 °C | 54.36 mm |
| February | -5.7 °C | 1.9 °C | 51.82 mm |
| March | -0.9 °C | 7.2 °C | 55.63 mm |
| April | 4.5 °C | 13.6 °C | 96.52 mm |
| May | 10.2 °C | 19.8 °C | 116.84 mm |
| June | 15.8 °C | 25.3 °C | 109.47 mm |
| July | 19.6 °C | 27.9 °C | 94.49 mm |
| August | 19.3 °C | 27.1 °C | 103.63 mm |
| September | 15.2 °C | 23.4 °C | 89.15 mm |
| October | 8.3 °C | 16.9 °C | 88.65 mm |
| November | 1.7 °C | 9.1 °C | 66.8 mm |
| December | -3.9 °C | 2.8 °C | 57.91 mm |
| Annual | 6.4 °C | 14.6 °C | 985.27 mm |
| Average First Frost Date | Oct. 21 - Oct. 31 |
| 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 |