Charter Oak, Iowa has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 37.5 °F (low) to 59.2 °F (high). Annual precipitation averages 32.4 Inches. 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 | 10.2 °F | 28.9 °F | 0.7 in. |
| February | 14.4 °F | 33.8 °F | 0.91 in. |
| March | 25.5 °F | 47.2 °F | 1.73 in. |
| April | 36.3 °F | 60.6 °F | 3.39 in. |
| May | 48.6 °F | 71.4 °F | 4.56 in. |
| June | 59.5 °F | 81.3 °F | 4.84 in. |
| July | 63.2 °F | 84.4 °F | 3.89 in. |
| August | 60.4 °F | 82.3 °F | 4.3 in. |
| September | 51.4 °F | 76.4 °F | 3.16 in. |
| October | 38.9 °F | 63.5 °F | 2.32 in. |
| November | 25.9 °F | 47.2 °F | 1.39 in. |
| December | 15.8 °F | 33.8 °F | 1.16 in. |
| Annual | 37.5 °F | 59.2 °F | 32.35 in. |
| 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 : -20°F to -15°F |
| Plant Hardiness Zone - 2012 | Zone 5a : -20°F to -15°F |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |