Northbrook, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 5.7 °C (low) to 14.8 °C (high). Annual precipitation averages 981.5 Millimeters. Northbrook is located in USDA Plant Hardiness Zone 6a. The growing season typically runs from the last frost around Apr. 11 - Apr. 20 through the first frost around Oct. 21 - Oct. 31.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -7.9 °C | -0.3 °C | 53.85 mm |
| February | -6.4 °C | 1.7 °C | 50.8 mm |
| March | -1.6 °C | 7.3 °C | 56.39 mm |
| April | 4.1 °C | 13.8 °C | 96.52 mm |
| May | 10.1 °C | 20.3 °C | 119.13 mm |
| June | 15.6 °C | 26 °C | 109.98 mm |
| July | 18.9 °C | 28.4 °C | 92.71 mm |
| August | 18.3 °C | 27.5 °C | 103.63 mm |
| September | 14 °C | 23.9 °C | 87.63 mm |
| October | 7.3 °C | 16.9 °C | 87.88 mm |
| November | 0.9 °C | 8.9 °C | 66.04 mm |
| December | -4.6 °C | 2.7 °C | 56.9 mm |
| Annual | 5.7 °C | 14.8 °C | 981.46 mm |
| Average First Frost Date | Oct. 21 - Oct. 31 |
| Average Last Frost Date | Apr. 11 - Apr. 20 |
| 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 | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |