Duncan, Oklahoma has a Humid Subtropical Climate climate (Köppen classification: Cfa). Average annual temperatures range from 50.1 °F (low) to 73.9 °F (high). Annual precipitation averages 35.7 Inches. Duncan is located in USDA Plant Hardiness Zone 8a. The growing season typically runs from the last frost around Mar. 21 - Mar. 31 through the first frost around Nov. 1 - Nov. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 28.3 °F | 52.5 °F | 1.45 in. |
| February | 31.9 °F | 56.4 °F | 1.75 in. |
| March | 40.6 °F | 65.5 °F | 2.68 in. |
| April | 48.5 °F | 73.3 °F | 3.38 in. |
| May | 58.8 °F | 81.0 °F | 5.13 in. |
| June | 67.8 °F | 89.3 °F | 4.37 in. |
| July | 71.6 °F | 94.7 °F | 2.47 in. |
| August | 70.7 °F | 94.8 °F | 2.82 in. |
| September | 62.9 °F | 86.4 °F | 3.73 in. |
| October | 50.7 °F | 75.7 °F | 3.69 in. |
| November | 39.4 °F | 63.9 °F | 2.25 in. |
| December | 30.3 °F | 53.6 °F | 2.01 in. |
| Annual | 50.1 °F | 73.9 °F | 35.73 in. |
| Average First Frost Date | Nov. 1 - Nov. 10 |
| Average Last Frost Date | Mar. 21 - Mar. 31 |
| Average Days With Frost | 50-75 Days |
| Plant Hardiness Zone | Zone 8a : 10°F to 15°F |
| Plant Hardiness Zone - 2012 | Zone 7b : 5°F to 10°F |
| Current Drought Conditions | Moderate Drought |
| Köppen Climate Classification | Cfa - Humid Subtropical Climate |