Barnum, Iowa has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 2.7 °C (low) to 14 °C (high). Annual precipitation averages 888.5 Millimeters. Barnum 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 | -12.9 °C | -3.2 °C | 22.1 mm |
| February | -10.7 °C | -0.8 °C | 28.7 mm |
| March | -4.1 °C | 6.7 °C | 51.05 mm |
| April | 2.1 °C | 14.9 °C | 94.74 mm |
| May | 9.2 °C | 21.2 °C | 125.73 mm |
| June | 15.2 °C | 26.7 °C | 134.62 mm |
| July | 17.2 °C | 28.3 °C | 102.11 mm |
| August | 15.6 °C | 27.1 °C | 114.05 mm |
| September | 10.4 °C | 23.7 °C | 78.23 mm |
| October | 3.6 °C | 16.6 °C | 63.25 mm |
| November | -3.4 °C | 7.4 °C | 40.89 mm |
| December | -9.5 °C | -0.2 °C | 33.02 mm |
| Annual | 2.7 °C | 14 °C | 888.49 mm |
| 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 : -28.9°C to -26.1°C |
| Plant Hardiness Zone - 2012 | Zone 5a : -28.9°C to -26.1°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |