Riverdale, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 42.6 °F (low) to 59.7 °F (high). Annual precipitation averages 39.8 Inches. Riverdale 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 | 18.2 °F | 32.4 °F | 2.21 in. |
| February | 20.9 °F | 36.0 °F | 2.09 in. |
| March | 29.9 °F | 46.4 °F | 2.38 in. |
| April | 40.1 °F | 59.1 °F | 3.86 in. |
| May | 51.0 °F | 70.0 °F | 4.47 in. |
| June | 61.1 °F | 80.0 °F | 4.52 in. |
| July | 66.2 °F | 84.1 °F | 4.38 in. |
| August | 64.6 °F | 82.3 °F | 4.16 in. |
| September | 57.0 °F | 76.2 °F | 3.25 in. |
| October | 44.9 °F | 63.4 °F | 3.49 in. |
| November | 33.9 °F | 49.4 °F | 2.7 in. |
| December | 23.8 °F | 37.6 °F | 2.29 in. |
| Annual | 42.6 °F | 59.7 °F | 39.8 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 6a : -10°F to -5°F |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |