Ottumwa, Iowa has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 5 °C (low) to 16.1 °C (high). Annual precipitation averages 997.5 Millimeters. 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 | -9.6 °C | -0.1 °C | 36.83 mm |
| February | -7.7 °C | 2.5 °C | 42.67 mm |
| March | -1.7 °C | 9.8 °C | 59.44 mm |
| April | 4.6 °C | 16.8 °C | 99.06 mm |
| May | 11 °C | 22.5 °C | 129.54 mm |
| June | 16.8 °C | 27.9 °C | 144.02 mm |
| July | 18.6 °C | 30 °C | 108.46 mm |
| August | 17.4 °C | 28.8 °C | 103.38 mm |
| September | 12.3 °C | 24.9 °C | 101.35 mm |
| October | 5.8 °C | 18.3 °C | 73.66 mm |
| November | -0.8 °C | 9.4 °C | 55.63 mm |
| December | -6.3 °C | 2.7 °C | 43.43 mm |
| Annual | 5 °C | 16.1 °C | 997.47 mm |
| 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 : -26.1°C to -23.3°C |
| Plant Hardiness Zone - 2012 | Zone 5b : -26.1°C to -23.3°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |