Ottumwa, Iowa has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 41.1 °F (low) to 61 °F (high). Annual precipitation averages 39.3 Inches. Ottumwa 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 | 14.7 °F | 31.8 °F | 1.45 in. |
| February | 18.2 °F | 36.5 °F | 1.68 in. |
| March | 29.0 °F | 49.7 °F | 2.34 in. |
| April | 40.2 °F | 62.3 °F | 3.9 in. |
| May | 51.8 °F | 72.5 °F | 5.1 in. |
| June | 62.2 °F | 82.2 °F | 5.67 in. |
| July | 65.4 °F | 86.0 °F | 4.27 in. |
| August | 63.3 °F | 83.9 °F | 4.07 in. |
| September | 54.2 °F | 76.8 °F | 3.99 in. |
| October | 42.5 °F | 64.9 °F | 2.9 in. |
| November | 30.6 °F | 49.0 °F | 2.19 in. |
| December | 20.7 °F | 36.8 °F | 1.71 in. |
| Annual | 41.1 °F | 61 °F | 39.27 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 |