Decatur, Indiana has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 40.9 °F (low) to 60.5 °F (high). Annual precipitation averages 39.9 Inches. 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 | 17.9 °F | 32.8 °F | 2.54 in. |
| February | 19.8 °F | 36.4 °F | 2.14 in. |
| March | 28.2 °F | 47.3 °F | 2.72 in. |
| April | 38.8 °F | 60.7 °F | 3.93 in. |
| May | 50.1 °F | 72.0 °F | 4.64 in. |
| June | 60.1 °F | 80.9 °F | 4.36 in. |
| July | 63.2 °F | 84.5 °F | 4.32 in. |
| August | 61.0 °F | 82.6 °F | 3.88 in. |
| September | 53.4 °F | 76.9 °F | 3.01 in. |
| October | 42.5 °F | 64.4 °F | 2.89 in. |
| November | 32.4 °F | 49.8 °F | 3.01 in. |
| December | 23.7 °F | 37.8 °F | 2.44 in. |
| Annual | 40.9 °F | 60.5 °F | 39.88 in. |
| 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 : -10°F to -5°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 |