Lake Forest, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 41.5 °F (low) to 57.4 °F (high). Annual precipitation averages 40.1 Inches. Lake Forest is located in USDA Plant Hardiness Zone 6a. The growing season typically runs from the last frost around Apr. 21 - Apr. 30 through the first frost around Oct. 21 - Oct. 31.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 16.8 °F | 30.8 °F | 2.13 in. |
| February | 19.7 °F | 34.3 °F | 2.06 in. |
| March | 28.5 °F | 44.2 °F | 2.32 in. |
| April | 38.2 °F | 55.3 °F | 4.2 in. |
| May | 48.5 °F | 66.7 °F | 4.71 in. |
| June | 58.5 °F | 76.8 °F | 4.29 in. |
| July | 65.2 °F | 81.7 °F | 4.03 in. |
| August | 64.7 °F | 80.3 °F | 3.95 in. |
| September | 56.9 °F | 73.6 °F | 4.18 in. |
| October | 44.8 °F | 61.5 °F | 3.4 in. |
| November | 33.3 °F | 47.7 °F | 2.75 in. |
| December | 23.0 °F | 36.2 °F | 2.09 in. |
| Annual | 41.5 °F | 57.4 °F | 40.11 in. |
| Average First Frost Date | Oct. 21 - Oct. 31 |
| Average Last Frost Date | Apr. 21 - Apr. 30 |
| 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 |