Lemont, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 5.2 °C (low) to 15.7 °C (high). Annual precipitation averages 1023.4 Millimeters. Lemont 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 | -8.5 °C | -0.2 °C | 56.13 mm |
| February | -7 °C | 2 °C | 52.58 mm |
| March | -1.7 °C | 8.5 °C | 62.99 mm |
| April | 4.2 °C | 15.8 °C | 101.6 mm |
| May | 10.2 °C | 21.9 °C | 123.44 mm |
| June | 15.8 °C | 27.3 °C | 116.33 mm |
| July | 18.2 °C | 29.5 °C | 108.71 mm |
| August | 17.3 °C | 28.4 °C | 105.92 mm |
| September | 13.1 °C | 25.1 °C | 84.07 mm |
| October | 6.3 °C | 17.6 °C | 90.93 mm |
| November | 0.2 °C | 9.6 °C | 63.75 mm |
| December | -5.3 °C | 2.7 °C | 56.9 mm |
| Annual | 5.2 °C | 15.7 °C | 1023.35 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 |