Allendale, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 45.2 °F (low) to 65.9 °F (high). Annual precipitation averages 47.4 Inches. Allendale is located in USDA Plant Hardiness Zone 6b. The growing season typically runs from the last frost around Apr. 1 - Apr. 10 through the first frost around Oct. 21 - Oct. 31.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 22.9 °F | 39.3 °F | 3.52 in. |
| February | 25.7 °F | 44.4 °F | 2.81 in. |
| March | 34.1 °F | 54.7 °F | 4.05 in. |
| April | 44.4 °F | 66.9 °F | 5.01 in. |
| May | 55.3 °F | 76.6 °F | 5.26 in. |
| June | 64.2 °F | 85.1 °F | 4.75 in. |
| July | 67.0 °F | 87.6 °F | 4.34 in. |
| August | 64.8 °F | 86.7 °F | 3.12 in. |
| September | 57.1 °F | 81.5 °F | 3.55 in. |
| October | 45.4 °F | 69.5 °F | 3.47 in. |
| November | 35.0 °F | 55.2 °F | 3.95 in. |
| December | 27.0 °F | 43.7 °F | 3.53 in. |
| Annual | 45.2 °F | 65.9 °F | 47.36 in. |
| Average First Frost Date | Oct. 21 - Oct. 31 |
| Average Last Frost Date | Apr. 1 - Apr. 10 |
| Average Days With Frost | 75-100 Days |
| Plant Hardiness Zone | Zone 6b : -5°F to 0°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 |