Round Lake Heights, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 3.8 °C (low) to 14.1 °C (high). Annual precipitation averages 966 Millimeters. Round Lake Heights is located in USDA Plant Hardiness Zone 5b. The growing season typically runs from the last frost around Apr. 21 - Apr. 30 through the first frost around Oct. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -10.1 °C | -1.6 °C | 48.51 mm |
| February | -8.5 °C | 0.6 °C | 49.02 mm |
| March | -3.3 °C | 6.8 °C | 57.4 mm |
| April | 2.5 °C | 13.8 °C | 98.55 mm |
| May | 8.5 °C | 20.2 °C | 113.28 mm |
| June | 14.1 °C | 25.7 °C | 119.13 mm |
| July | 16.9 °C | 28.1 °C | 96.52 mm |
| August | 16.1 °C | 27.1 °C | 96.01 mm |
| September | 11.7 °C | 23.3 °C | 91.44 mm |
| October | 5.3 °C | 16.1 °C | 80.52 mm |
| November | -0.8 °C | 8.2 °C | 60.96 mm |
| December | -6.6 °C | 1.4 °C | 54.61 mm |
| Annual | 3.8 °C | 14.1 °C | 965.95 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 21 - Apr. 30 |
| Average Days With Frost | 125-150 Days |
| Plant Hardiness Zone | Zone 5b : -26.1°C to -23.3°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 |