Irondale, Missouri has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 7 °C (low) to 19.2 °C (high). Annual precipitation averages 1147.1 Millimeters. Irondale is located in USDA Plant Hardiness Zone 6b. 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 | -5.3 °C | 5.4 °C | 67.82 mm |
| February | -3.6 °C | 8.4 °C | 67.31 mm |
| March | 0.9 °C | 13.8 °C | 98.55 mm |
| April | 6.6 °C | 20 °C | 134.37 mm |
| May | 12.1 °C | 24.4 °C | 136.65 mm |
| June | 16.7 °C | 28.8 °C | 104.65 mm |
| July | 19.1 °C | 30.8 °C | 99.06 mm |
| August | 18 °C | 30.6 °C | 90.17 mm |
| September | 13.6 °C | 26.8 °C | 85.6 mm |
| October | 7.1 °C | 20.8 °C | 85.85 mm |
| November | 1.3 °C | 13.3 °C | 100.33 mm |
| December | -3 °C | 7.3 °C | 76.71 mm |
| Annual | 7 °C | 19.2 °C | 1147.07 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 11 - Apr. 20 |
| Average Days With Frost | 100-125 Days |
| Plant Hardiness Zone | Zone 6b : -20.6°C to -17.8°C |
| Plant Hardiness Zone - 2012 | Zone 6a : -23.3°C to -20.6°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |