River Forest, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 42.4 °F (low) to 59.3 °F (high). Annual precipitation averages 39.1 Inches. River Forest 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 | 31.6 °F | 2.16 in. |
| February | 20.4 °F | 35.3 °F | 2.09 in. |
| March | 29.6 °F | 46.1 °F | 2.33 in. |
| April | 39.9 °F | 58.5 °F | 3.97 in. |
| May | 50.8 °F | 69.7 °F | 4.67 in. |
| June | 61.0 °F | 79.8 °F | 4.33 in. |
| July | 66.3 °F | 84.2 °F | 3.93 in. |
| August | 64.9 °F | 82.3 °F | 4.06 in. |
| September | 57.0 °F | 75.7 °F | 3.29 in. |
| October | 44.6 °F | 62.9 °F | 3.42 in. |
| November | 33.3 °F | 48.9 °F | 2.57 in. |
| December | 23.4 °F | 37.1 °F | 2.29 in. |
| Annual | 42.4 °F | 59.3 °F | 39.11 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 |