Saybrook, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 40.9 °F (low) to 61.1 °F (high). Annual precipitation averages 38.4 Inches. Saybrook 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. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 16.4 °F | 32.6 °F | 2.22 in. |
| February | 19.5 °F | 37.1 °F | 1.89 in. |
| March | 28.7 °F | 48.8 °F | 2.61 in. |
| April | 39.5 °F | 62.1 °F | 3.72 in. |
| May | 51.6 °F | 73.2 °F | 4.46 in. |
| June | 61.1 °F | 81.6 °F | 4.39 in. |
| July | 63.7 °F | 84.2 °F | 4.04 in. |
| August | 61.3 °F | 82.8 °F | 3.51 in. |
| September | 53.6 °F | 77.9 °F | 3.3 in. |
| October | 42.1 °F | 65.2 °F | 3.3 in. |
| November | 31.2 °F | 50.2 °F | 2.73 in. |
| December | 21.8 °F | 37.5 °F | 2.19 in. |
| Annual | 40.9 °F | 61.1 °F | 38.36 in. |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| 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 | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |