Irwin, South Carolina has a Humid Subtropical Climate climate (Köppen classification: Cfa). Average annual temperatures range from 10.2 °C (low) to 22.7 °C (high). Annual precipitation averages 1126.8 Millimeters. Irwin 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 | -0.3 °C | 12 °C | 95.76 mm |
| February | 1.1 °C | 14.1 °C | 82.3 mm |
| March | 4.6 °C | 18.3 °C | 102.11 mm |
| April | 9.3 °C | 23.2 °C | 84.58 mm |
| May | 14.6 °C | 26.9 °C | 82.3 mm |
| June | 18.9 °C | 30.8 °C | 105.41 mm |
| July | 20.9 °C | 32.6 °C | 99.57 mm |
| August | 20.4 °C | 31.7 °C | 114.55 mm |
| September | 17.1 °C | 28.8 °C | 95.5 mm |
| October | 10.2 °C | 23.3 °C | 80.26 mm |
| November | 4.3 °C | 17.7 °C | 85.6 mm |
| December | 1.3 °C | 13.3 °C | 98.81 mm |
| Annual | 10.2 °C | 22.7 °C | 1126.75 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 8a : -12.2°C to -9.4°C |
| Current Drought Conditions | Moderate Drought |
| Köppen Climate Classification | Cfa - Humid Subtropical Climate |