Irena, Missouri has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 4.6 °C (low) to 16.2 °C (high). Annual precipitation averages 965.5 Millimeters. Irena 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 | -10.2 °C | 0.2 °C | 22.1 mm |
| February | -7.7 °C | 3.2 °C | 34.04 mm |
| March | -2 °C | 10.1 °C | 56.9 mm |
| April | 4.1 °C | 16.8 °C | 98.3 mm |
| May | 10.6 °C | 22.3 °C | 139.19 mm |
| June | 16.1 °C | 27.2 °C | 136.4 mm |
| July | 18.4 °C | 29.8 °C | 118.36 mm |
| August | 17.2 °C | 28.9 °C | 104.39 mm |
| September | 12.2 °C | 24.9 °C | 90.68 mm |
| October | 5.3 °C | 18.2 °C | 78.23 mm |
| November | -1.3 °C | 9.8 °C | 51.31 mm |
| December | -7 °C | 2.9 °C | 35.56 mm |
| Annual | 4.6 °C | 16.2 °C | 965.46 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 |