Prospect Heights, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 5 °C (low) to 14.9 °C (high). Annual precipitation averages 954.5 Millimeters. Prospect Heights 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 | -8.8 °C | -0.5 °C | 51.56 mm |
| February | -7.3 °C | 1.7 °C | 49.53 mm |
| March | -2.1 °C | 7.7 °C | 57.4 mm |
| April | 3.6 °C | 14.3 °C | 95.25 mm |
| May | 9.6 °C | 20.7 °C | 114.81 mm |
| June | 15.2 °C | 26.3 °C | 111.51 mm |
| July | 18.2 °C | 28.7 °C | 92.46 mm |
| August | 17.4 °C | 27.7 °C | 101.85 mm |
| September | 12.9 °C | 23.9 °C | 83.06 mm |
| October | 6.3 °C | 16.8 °C | 81.79 mm |
| November | 0 °C | 8.9 °C | 61.21 mm |
| December | -5.4 °C | 2.4 °C | 54.1 mm |
| Annual | 5 °C | 14.9 °C | 954.53 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 | Abnormally Dry |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |