Swan, Iowa has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 4.9 °C (low) to 15.9 °C (high). Annual precipitation averages 923 Millimeters. Swan 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 | -10.3 °C | -0.5 °C | 25.15 mm |
| February | -8.3 °C | 2.1 °C | 33.53 mm |
| March | -2.1 °C | 9.2 °C | 52.07 mm |
| April | 4.4 °C | 16.8 °C | 97.54 mm |
| May | 11.2 °C | 22.1 °C | 130.05 mm |
| June | 16.8 °C | 27.6 °C | 133.35 mm |
| July | 18.9 °C | 29.6 °C | 109.98 mm |
| August | 17.5 °C | 28.9 °C | 106.93 mm |
| September | 12.7 °C | 25.1 °C | 90.68 mm |
| October | 5.8 °C | 17.7 °C | 66.04 mm |
| November | -1.2 °C | 9.4 °C | 44.7 mm |
| December | -7.2 °C | 2.3 °C | 33.02 mm |
| Annual | 4.9 °C | 15.9 °C | 923.04 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 |