Round Lake Beach, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 3.9 °C (low) to 14.2 °C (high). Annual precipitation averages 965.7 Millimeters. Round Lake Beach 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 | -9.9 °C | -1.4 °C | 48.77 mm |
| February | -8.4 °C | 0.6 °C | 49.28 mm |
| March | -3.2 °C | 6.8 °C | 57.66 mm |
| April | 2.6 °C | 13.8 °C | 98.81 mm |
| May | 8.6 °C | 20.2 °C | 113.03 mm |
| June | 14.2 °C | 25.7 °C | 118.36 mm |
| July | 16.9 °C | 28.1 °C | 96.52 mm |
| August | 16.1 °C | 27.1 °C | 95.76 mm |
| September | 11.9 °C | 23.3 °C | 91.19 mm |
| October | 5.4 °C | 16.1 °C | 80.52 mm |
| November | -0.8 °C | 8.2 °C | 60.96 mm |
| December | -6.5 °C | 1.5 °C | 54.86 mm |
| Annual | 3.9 °C | 14.2 °C | 965.72 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 | Abnormally Dry |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |