Grayslake, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 39.4 °F (low) to 57.6 °F (high). Annual precipitation averages 38 Inches. Grayslake 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 | 14.5 °F | 29.6 °F | 1.94 in. |
| February | 17.2 °F | 33.5 °F | 1.97 in. |
| March | 26.7 °F | 44.4 °F | 2.3 in. |
| April | 36.9 °F | 56.8 °F | 3.9 in. |
| May | 47.7 °F | 68.2 °F | 4.45 in. |
| June | 57.8 °F | 78.1 °F | 4.57 in. |
| July | 62.8 °F | 82.5 °F | 3.79 in. |
| August | 61.4 °F | 80.8 °F | 3.73 in. |
| September | 53.6 °F | 74.0 °F | 3.55 in. |
| October | 42.0 °F | 61.1 °F | 3.21 in. |
| November | 30.9 °F | 47.0 °F | 2.43 in. |
| December | 20.7 °F | 35.0 °F | 2.15 in. |
| Annual | 39.4 °F | 57.6 °F | 37.99 in. |
| 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 : -15°F to -10°F |
| Plant Hardiness Zone - 2012 | Zone 5b : -15°F to -10°F |
| Current Drought Conditions | Moderate Drought |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |