Decorah, Iowa has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 2.3 °C (low) to 13.7 °C (high). Annual precipitation averages 947.4 Millimeters. Decorah is located in USDA Plant Hardiness Zone 5a. The growing season typically runs from the last frost around May 1 - May 10 through the first frost around Oct. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -13.1 °C | -3.6 °C | 25.15 mm |
| February | -11.2 °C | -1.1 °C | 27.69 mm |
| March | -4.6 °C | 6 °C | 49.53 mm |
| April | 1.8 °C | 14.4 °C | 100.58 mm |
| May | 8.3 °C | 20.9 °C | 121.92 mm |
| June | 14.1 °C | 26.2 °C | 155.45 mm |
| July | 16.1 °C | 28.1 °C | 112.52 mm |
| August | 14.8 °C | 26.9 °C | 110.49 mm |
| September | 10.3 °C | 23.4 °C | 92.71 mm |
| October | 3.4 °C | 16.2 °C | 69.09 mm |
| November | -3 °C | 6.9 °C | 47.5 mm |
| December | -9.1 °C | -0.4 °C | 34.8 mm |
| Annual | 2.3 °C | 13.7 °C | 947.43 mm |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | 150-180 Days |
| Plant Hardiness Zone | Zone 5a : -28.9°C to -26.1°C |
| Plant Hardiness Zone - 2012 | Zone 4b : -31.7°C to -28.9°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |