Lemont, Pennsylvania has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 3.9 °C (low) to 15.4 °C (high). Annual precipitation averages 1034.8 Millimeters. Lemont is located in USDA Plant Hardiness Zone 6b. The growing season typically runs from the last frost around Apr. 21 - Apr. 30 through the first frost around Oct. 21 - Oct. 31.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -7.7 °C | 1.4 °C | 68.33 mm |
| February | -7.2 °C | 3.2 °C | 56.64 mm |
| March | -3.2 °C | 8.1 °C | 83.57 mm |
| April | 2.6 °C | 15.6 °C | 90.42 mm |
| May | 8.3 °C | 21.4 °C | 98.04 mm |
| June | 13.3 °C | 25.7 °C | 99.82 mm |
| July | 15.7 °C | 28.1 °C | 97.03 mm |
| August | 14.7 °C | 27.1 °C | 101.09 mm |
| September | 10.6 °C | 23.2 °C | 103.89 mm |
| October | 4.5 °C | 16.6 °C | 91.44 mm |
| November | -0.6 °C | 10.1 °C | 66.55 mm |
| December | -4.7 °C | 3.9 °C | 77.98 mm |
| Annual | 3.9 °C | 15.4 °C | 1034.8 mm |
| Average First Frost Date | Oct. 21 - Oct. 31 |
| Average Last Frost Date | Apr. 21 - Apr. 30 |
| Average Days With Frost | 100-125 Days |
| Plant Hardiness Zone | Zone 6b : -20.6°C to -17.8°C |
| Plant Hardiness Zone - 2012 | Zone 6b : -20.6°C to -17.8°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |