McHenry, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 3.5 °C (low) to 14.4 °C (high). Annual precipitation averages 966.7 Millimeters. McHenry 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 | -10.4 °C | -1.6 °C | 45.21 mm |
| February | -8.8 °C | 0.6 °C | 46.74 mm |
| March | -3.5 °C | 7 °C | 56.13 mm |
| April | 2.3 °C | 14.3 °C | 95.25 mm |
| May | 8.4 °C | 20.7 °C | 118.87 mm |
| June | 14 °C | 26.1 °C | 124.97 mm |
| July | 16.6 °C | 28.3 °C | 98.55 mm |
| August | 15.7 °C | 27.3 °C | 98.3 mm |
| September | 11.2 °C | 23.6 °C | 90.93 mm |
| October | 4.7 °C | 16.3 °C | 79.76 mm |
| November | -1.2 °C | 8.3 °C | 61.21 mm |
| December | -6.9 °C | 1.4 °C | 50.8 mm |
| Annual | 3.5 °C | 14.4 °C | 966.72 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 | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |