Decatur, Indiana has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 5 °C (low) to 15.8 °C (high). Annual precipitation averages 1013 Millimeters. Decatur is located in USDA Plant Hardiness Zone 6a. 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 | -7.8 °C | 0.4 °C | 64.52 mm |
| February | -6.8 °C | 2.4 °C | 54.36 mm |
| March | -2.1 °C | 8.5 °C | 69.09 mm |
| April | 3.8 °C | 15.9 °C | 99.82 mm |
| May | 10.1 °C | 22.2 °C | 117.86 mm |
| June | 15.6 °C | 27.2 °C | 110.74 mm |
| July | 17.3 °C | 29.2 °C | 109.73 mm |
| August | 16.1 °C | 28.1 °C | 98.55 mm |
| September | 11.9 °C | 24.9 °C | 76.45 mm |
| October | 5.8 °C | 18 °C | 73.41 mm |
| November | 0.2 °C | 9.9 °C | 76.45 mm |
| December | -4.6 °C | 3.2 °C | 61.98 mm |
| Annual | 5 °C | 15.8 °C | 1012.96 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 21 - Apr. 30 |
| Average Days With Frost | 100-125 Days |
| Plant Hardiness Zone | Zone 6a : -23.3°C to -20.6°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 |