Crystal Lake, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 38.9 °F (low) to 58.6 °F (high). Annual precipitation averages 38.9 Inches. Crystal Lake 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 | 30.4 °F | 1.85 in. |
| February | 17.2 °F | 35.0 °F | 1.89 in. |
| March | 26.6 °F | 46.4 °F | 2.18 in. |
| April | 36.4 °F | 58.2 °F | 3.75 in. |
| May | 47.5 °F | 69.7 °F | 4.88 in. |
| June | 57.6 °F | 79.4 °F | 5.03 in. |
| July | 61.9 °F | 83.3 °F | 4.07 in. |
| August | 60.2 °F | 81.4 °F | 3.99 in. |
| September | 52.6 °F | 74.7 °F | 3.55 in. |
| October | 41.6 °F | 61.6 °F | 3.16 in. |
| November | 30.5 °F | 47.6 °F | 2.46 in. |
| December | 20.1 °F | 35.0 °F | 2.05 in. |
| Annual | 38.9 °F | 58.6 °F | 38.86 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 | Abnormally Dry |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |