Westmont, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 4.8 °C (low) to 15.7 °C (high). Annual precipitation averages 1017.3 Millimeters. Westmont 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 | -8.9 °C | -0.1 °C | 56.13 mm |
| February | -7.4 °C | 2.1 °C | 54.1 mm |
| March | -2.2 °C | 8.7 °C | 60.45 mm |
| April | 3.5 °C | 15.7 °C | 101.35 mm |
| May | 9.6 °C | 21.9 °C | 122.17 mm |
| June | 15.2 °C | 27.3 °C | 114.81 mm |
| July | 17.8 °C | 29.7 °C | 101.6 mm |
| August | 17 °C | 28.6 °C | 106.68 mm |
| September | 12.7 °C | 24.9 °C | 85.09 mm |
| October | 5.8 °C | 17.6 °C | 90.93 mm |
| November | -0.3 °C | 9.3 °C | 65.79 mm |
| December | -5.8 °C | 2.6 °C | 58.17 mm |
| Annual | 4.8 °C | 15.7 °C | 1017.27 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 |