Algonquin, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 4.1 °C (low) to 14.8 °C (high). Annual precipitation averages 997.7 Millimeters. Algonquin 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 | -9.7 °C | -1.1 °C | 48.77 mm |
| February | -8.2 °C | 1.1 °C | 48.26 mm |
| March | -2.8 °C | 7.5 °C | 55.37 mm |
| April | 2.9 °C | 14.7 °C | 95.25 mm |
| May | 9 °C | 21 °C | 128.02 mm |
| June | 14.6 °C | 26.5 °C | 126.24 mm |
| July | 17.2 °C | 28.7 °C | 103.89 mm |
| August | 16.4 °C | 27.6 °C | 104.14 mm |
| September | 11.9 °C | 23.9 °C | 89.41 mm |
| October | 5.4 °C | 16.7 °C | 81.28 mm |
| November | -0.7 °C | 8.6 °C | 63.25 mm |
| December | -6.3 °C | 1.9 °C | 53.85 mm |
| Annual | 4.1 °C | 14.8 °C | 997.73 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 |