Cullom, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 4.8 °C (low) to 16.2 °C (high). Annual precipitation averages 975.9 Millimeters. Cullom is located in USDA Plant Hardiness Zone 5b. The growing season typically runs from the last frost around Apr. 21 - Apr. 30 through the first frost around Oct. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -8.8 °C | 0.2 °C | 55.88 mm |
| February | -7.1 °C | 2.7 °C | 47.75 mm |
| March | -1.8 °C | 9.4 °C | 65.28 mm |
| April | 3.9 °C | 16.9 °C | 95 mm |
| May | 10.4 °C | 23 °C | 114.05 mm |
| June | 15.8 °C | 27.8 °C | 113.79 mm |
| July | 17.6 °C | 29.3 °C | 109.98 mm |
| August | 16.2 °C | 28.4 °C | 93.47 mm |
| September | 11.7 °C | 25.6 °C | 77.47 mm |
| October | 5.4 °C | 18.6 °C | 81.79 mm |
| November | -0.4 °C | 10.1 °C | 68.83 mm |
| December | -5.8 °C | 2.9 °C | 52.58 mm |
| Annual | 4.8 °C | 16.2 °C | 975.87 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 21 - Apr. 30 |
| Average Days With Frost | 125-150 Days |
| Plant Hardiness Zone | Zone 5b : -26.1°C to -23.3°C |
| Plant Hardiness Zone - 2012 | Zone 5b : -26.1°C to -23.3°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |