Allendale, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 7.3 °C (low) to 18.9 °C (high). Annual precipitation averages 1202.9 Millimeters. 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 | -5.1 °C | 4.1 °C | 89.41 mm |
| February | -3.5 °C | 6.9 °C | 71.37 mm |
| March | 1.2 °C | 12.6 °C | 102.87 mm |
| April | 6.9 °C | 19.4 °C | 127.25 mm |
| May | 12.9 °C | 24.8 °C | 133.6 mm |
| June | 17.9 °C | 29.5 °C | 120.65 mm |
| July | 19.4 °C | 30.9 °C | 110.24 mm |
| August | 18.2 °C | 30.4 °C | 79.25 mm |
| September | 13.9 °C | 27.5 °C | 90.17 mm |
| October | 7.4 °C | 20.8 °C | 88.14 mm |
| November | 1.7 °C | 12.9 °C | 100.33 mm |
| December | -2.8 °C | 6.5 °C | 89.66 mm |
| Annual | 7.3 °C | 18.9 °C | 1202.94 mm |
| 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 : -20.6°C to -17.8°C |
| Plant Hardiness Zone - 2012 | Zone 6a : -23.3°C to -20.6°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |