Mount Prospect, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 5 °C (low) to 15 °C (high). Annual precipitation averages 958.6 Millimeters. Mount Prospect 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 | -8.7 °C | -0.4 °C | 51.82 mm |
| February | -7.2 °C | 1.7 °C | 49.02 mm |
| March | -2.1 °C | 7.7 °C | 57.66 mm |
| April | 3.6 °C | 14.4 °C | 95.25 mm |
| May | 9.7 °C | 20.7 °C | 116.33 mm |
| June | 15.2 °C | 26.3 °C | 111.76 mm |
| July | 18.2 °C | 28.7 °C | 92.2 mm |
| August | 17.4 °C | 27.7 °C | 102.11 mm |
| September | 12.9 °C | 24 °C | 83.57 mm |
| October | 6.3 °C | 16.9 °C | 81.53 mm |
| November | 0.1 °C | 9.1 °C | 62.48 mm |
| December | -5.4 °C | 2.6 °C | 54.86 mm |
| Annual | 5 °C | 15 °C | 958.59 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 |