Westmont, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 40.5 °F (low) to 60.2 °F (high). Annual precipitation averages 40.1 Inches. 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 | 15.9 °F | 31.8 °F | 2.21 in. |
| February | 18.6 °F | 35.8 °F | 2.13 in. |
| March | 28.0 °F | 47.7 °F | 2.38 in. |
| April | 38.3 °F | 60.2 °F | 3.99 in. |
| May | 49.2 °F | 71.4 °F | 4.81 in. |
| June | 59.3 °F | 81.2 °F | 4.52 in. |
| July | 64.0 °F | 85.4 °F | 4.0 in. |
| August | 62.6 °F | 83.4 °F | 4.2 in. |
| September | 54.8 °F | 76.9 °F | 3.35 in. |
| October | 42.5 °F | 63.6 °F | 3.58 in. |
| November | 31.5 °F | 48.7 °F | 2.59 in. |
| December | 21.6 °F | 36.6 °F | 2.29 in. |
| Annual | 40.5 °F | 60.2 °F | 40.05 in. |
| 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 : -10°F to -5°F |
| Plant Hardiness Zone - 2012 | Zone 5b : -15°F to -10°F |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |