Charter Oak, Iowa has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 3.1 °C (low) to 15.1 °C (high). Annual precipitation averages 821.7 Millimeters. Charter Oak 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 | -12.1 °C | -1.7 °C | 17.78 mm |
| February | -9.8 °C | 1 °C | 23.11 mm |
| March | -3.6 °C | 8.4 °C | 43.94 mm |
| April | 2.4 °C | 15.9 °C | 86.11 mm |
| May | 9.2 °C | 21.9 °C | 115.82 mm |
| June | 15.3 °C | 27.4 °C | 122.94 mm |
| July | 17.3 °C | 29.1 °C | 98.81 mm |
| August | 15.8 °C | 27.9 °C | 109.22 mm |
| September | 10.8 °C | 24.7 °C | 80.26 mm |
| October | 3.8 °C | 17.5 °C | 58.93 mm |
| November | -3.4 °C | 8.4 °C | 35.31 mm |
| December | -9 °C | 1 °C | 29.46 mm |
| Annual | 3.1 °C | 15.1 °C | 821.69 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 | Abnormally Dry |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |