Decatur City, Iowa has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 39.7 °F (low) to 60.3 °F (high). Annual precipitation averages 38.5 Inches. Decatur City is located in USDA Plant Hardiness Zone 5b. The growing season typically runs from the last frost around Apr. 11 - Apr. 20 through the first frost around Oct. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 13.2 °F | 31.7 °F | 0.99 in. |
| February | 17.1 °F | 36.6 °F | 1.41 in. |
| March | 27.9 °F | 49.2 °F | 2.25 in. |
| April | 38.6 °F | 61.2 °F | 4.01 in. |
| May | 50.4 °F | 71.0 °F | 5.4 in. |
| June | 60.5 °F | 80.5 °F | 5.19 in. |
| July | 64.7 °F | 84.9 °F | 4.53 in. |
| August | 62.2 °F | 83.3 °F | 4.37 in. |
| September | 53.1 °F | 76.0 °F | 3.8 in. |
| October | 40.9 °F | 63.8 °F | 3.02 in. |
| November | 28.9 °F | 49.0 °F | 2.06 in. |
| December | 18.8 °F | 36.7 °F | 1.47 in. |
| Annual | 39.7 °F | 60.3 °F | 38.5 in. |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 11 - Apr. 20 |
| Average Days With Frost | 125-150 Days |
| Plant Hardiness Zone | Zone 5b : -15°F to -10°F |
| Plant Hardiness Zone - 2012 | Zone 5b : -15°F to -10°F |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |