Rosemont, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 5.4 °C (low) to 15.1 °C (high). Annual precipitation averages 970.6 Millimeters. Rosemont is located in USDA Plant Hardiness Zone 6a. 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 | -8.3 °C | -0.2 °C | 53.09 mm |
| February | -6.8 °C | 1.9 °C | 50.29 mm |
| March | -1.7 °C | 7.8 °C | 58.17 mm |
| April | 3.9 °C | 14.5 °C | 97.03 mm |
| May | 10 °C | 20.8 °C | 117.86 mm |
| June | 15.6 °C | 26.4 °C | 112.27 mm |
| July | 18.6 °C | 28.8 °C | 91.95 mm |
| August | 17.8 °C | 27.8 °C | 101.09 mm |
| September | 13.3 °C | 24.1 °C | 84.33 mm |
| October | 6.6 °C | 16.9 °C | 83.57 mm |
| November | 0.3 °C | 9.1 °C | 64.52 mm |
| December | -5.1 °C | 2.7 °C | 56.39 mm |
| Annual | 5.4 °C | 15.1 °C | 970.56 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 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 |