Warren, Illinois has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 37.8 °F (low) to 56.9 °F (high). Annual precipitation averages 38.6 Inches. Warren is located in USDA Plant Hardiness Zone 5a. The growing season typically runs from the last frost around Apr. 21 - Apr. 30 through the first frost around Oct. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 11.2 °F | 27.2 °F | 1.4 in. |
| February | 14.6 °F | 31.5 °F | 1.58 in. |
| March | 25.4 °F | 43.9 °F | 2.15 in. |
| April | 36.4 °F | 57.8 °F | 3.88 in. |
| May | 48.2 °F | 69.4 °F | 4.33 in. |
| June | 58.3 °F | 78.7 °F | 5.67 in. |
| July | 61.7 °F | 81.7 °F | 4.59 in. |
| August | 59.6 °F | 80.1 °F | 4.14 in. |
| September | 51.3 °F | 73.7 °F | 3.67 in. |
| October | 39.8 °F | 60.9 °F | 2.96 in. |
| November | 28.8 °F | 45.6 °F | 2.41 in. |
| December | 17.8 °F | 32.7 °F | 1.78 in. |
| Annual | 37.8 °F | 56.9 °F | 38.56 in. |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | Apr. 21 - Apr. 30 |
| Average Days With Frost | 125-150 Days |
| Plant Hardiness Zone | Zone 5a : -20°F to -15°F |
| Plant Hardiness Zone - 2012 | Zone 5a : -20°F to -15°F |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |