Holcomb, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 3.5 °C (low) to 14.5 °C (high). Annual precipitation averages 957.8 Millimeters. Holcomb 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 | -10.8 °C | -1.9 °C | 42.16 mm |
| February | -8.9 °C | 0.4 °C | 42.67 mm |
| March | -3.2 °C | 7.3 °C | 56.39 mm |
| April | 2.7 °C | 15 °C | 92.71 mm |
| May | 9.2 °C | 21.3 °C | 117.86 mm |
| June | 14.7 °C | 26.4 °C | 132.59 mm |
| July | 16.7 °C | 28.1 °C | 103.63 mm |
| August | 15.6 °C | 27.2 °C | 102.62 mm |
| September | 10.9 °C | 23.9 °C | 87.88 mm |
| October | 4.4 °C | 16.7 °C | 72.39 mm |
| November | -1.6 °C | 8.3 °C | 58.42 mm |
| December | -7.4 °C | 1.2 °C | 48.51 mm |
| Annual | 3.5 °C | 14.5 °C | 957.83 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 5a : -28.9°C to -26.1°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |