Decorah, Iowa has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 36.2 °F (low) to 56.6 °F (high). Annual precipitation averages 37.3 Inches. 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 | 8.4 °F | 25.5 °F | 0.99 in. |
| February | 11.8 °F | 30.0 °F | 1.09 in. |
| March | 23.8 °F | 42.8 °F | 1.95 in. |
| April | 35.2 °F | 58.0 °F | 3.96 in. |
| May | 46.9 °F | 69.7 °F | 4.8 in. |
| June | 57.3 °F | 79.2 °F | 6.12 in. |
| July | 60.9 °F | 82.5 °F | 4.43 in. |
| August | 58.7 °F | 80.5 °F | 4.35 in. |
| September | 50.5 °F | 74.2 °F | 3.65 in. |
| October | 38.2 °F | 61.1 °F | 2.72 in. |
| November | 26.6 °F | 44.5 °F | 1.87 in. |
| December | 15.6 °F | 31.2 °F | 1.37 in. |
| Annual | 36.2 °F | 56.6 °F | 37.3 in. |
| 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 : -20°F to -15°F |
| Plant Hardiness Zone - 2012 | Zone 4b : -25°F to -20°F |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |