Northbrook, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 42.3 °F (low) to 58.6 °F (high). Annual precipitation averages 38.6 Inches. 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 | 17.7 °F | 31.4 °F | 2.12 in. |
| February | 20.4 °F | 35.1 °F | 2.0 in. |
| March | 29.2 °F | 45.1 °F | 2.22 in. |
| April | 39.3 °F | 56.8 °F | 3.8 in. |
| May | 50.2 °F | 68.6 °F | 4.69 in. |
| June | 60.1 °F | 78.8 °F | 4.33 in. |
| July | 66.0 °F | 83.2 °F | 3.65 in. |
| August | 65.0 °F | 81.5 °F | 4.08 in. |
| September | 57.2 °F | 75.0 °F | 3.45 in. |
| October | 45.2 °F | 62.5 °F | 3.46 in. |
| November | 33.6 °F | 48.1 °F | 2.6 in. |
| December | 23.8 °F | 36.8 °F | 2.24 in. |
| Annual | 42.3 °F | 58.6 °F | 38.64 in. |
| 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 : -10°F to -5°F |
| Plant Hardiness Zone - 2012 | Zone 5b : -15°F to -10°F |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |