River Sioux, Iowa has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 38.2 °F (low) to 60.9 °F (high). Annual precipitation averages 34.3 Inches. River Sioux is located in USDA Plant Hardiness Zone 5a. The growing season typically runs from the last frost around Apr. 21 - Apr. 30 through the first frost around Oct. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 11.2 °F | 30.8 °F | 0.76 in. |
| February | 15.0 °F | 35.5 °F | 0.98 in. |
| March | 26.2 °F | 49.0 °F | 1.97 in. |
| April | 37.0 °F | 62.3 °F | 3.65 in. |
| May | 49.6 °F | 72.9 °F | 4.64 in. |
| June | 60.4 °F | 83.0 °F | 5.12 in. |
| July | 64.1 °F | 86.3 °F | 3.79 in. |
| August | 61.2 °F | 84.0 °F | 4.23 in. |
| September | 52.0 °F | 78.0 °F | 3.8 in. |
| October | 39.0 °F | 64.7 °F | 2.49 in. |
| November | 26.3 °F | 49.2 °F | 1.58 in. |
| December | 16.1 °F | 35.3 °F | 1.31 in. |
| Annual | 38.2 °F | 60.9 °F | 34.32 in. |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | Apr. 21 - Apr. 30 |
| Average Days With Frost | 125-150 Days |
| Plant Hardiness Zone | Zone 5a : -20°F to -15°F |
| Plant Hardiness Zone - 2012 | Zone 5a : -20°F to -15°F |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |