Duncan, South Carolina has a Humid Subtropical Climate climate (Köppen classification: Cfa). Average annual temperatures range from 10.1 °C (low) to 22.2 °C (high). Annual precipitation averages 1336.6 Millimeters. 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 | -0.1 °C | 11.3 °C | 112.78 mm |
| February | 1.2 °C | 13.6 °C | 101.35 mm |
| March | 4.8 °C | 17.7 °C | 120.4 mm |
| April | 9.2 °C | 22.6 °C | 111.76 mm |
| May | 14.1 °C | 26.6 °C | 102.87 mm |
| June | 18.6 °C | 30.2 °C | 116.33 mm |
| July | 20.6 °C | 32.2 °C | 116.59 mm |
| August | 20 °C | 31.1 °C | 125.73 mm |
| September | 16.8 °C | 28.1 °C | 104.65 mm |
| October | 10.1 °C | 22.7 °C | 99.31 mm |
| November | 4.2 °C | 17.1 °C | 103.38 mm |
| December | 1.3 °C | 12.6 °C | 121.41 mm |
| Annual | 10.1 °C | 22.2 °C | 1336.56 mm |
| 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 : -12.2°C to -9.4°C |
| Plant Hardiness Zone - 2012 | Zone 7b : -15°C to -12.2°C |
| Current Drought Conditions | Severe Drought |
| Köppen Climate Classification | Cfa - Humid Subtropical Climate |