Berwyn, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 6.1 °C (low) to 15.3 °C (high). Annual precipitation averages 1005.3 Millimeters. Berwyn 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 | -7.7 °C | -0.1 °C | 55.12 mm |
| February | -6.2 °C | 2 °C | 52.58 mm |
| March | -1.2 °C | 7.9 °C | 59.69 mm |
| April | 4.6 °C | 14.8 °C | 100.84 mm |
| May | 10.7 °C | 21.1 °C | 119.63 mm |
| June | 16.3 °C | 26.6 °C | 110.24 mm |
| July | 19.3 °C | 29.1 °C | 109.22 mm |
| August | 18.6 °C | 28 °C | 104.39 mm |
| September | 14.4 °C | 24.4 °C | 82.8 mm |
| October | 7.6 °C | 17.3 °C | 87.12 mm |
| November | 1.1 °C | 9.4 °C | 64.77 mm |
| December | -4.6 °C | 2.9 °C | 58.93 mm |
| Annual | 6.1 °C | 15.3 °C | 1005.33 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 6a : -23.3°C to -20.6°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |