Irwin, South Carolina has a Humid Subtropical Climate climate (Köppen classification: Cfa). Average annual temperatures range from 50.4 °F (low) to 72.9 °F (high). Annual precipitation averages 44.4 Inches. 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 | 31.5 °F | 53.6 °F | 3.77 in. |
| February | 33.9 °F | 57.3 °F | 3.24 in. |
| March | 40.2 °F | 64.9 °F | 4.02 in. |
| April | 48.8 °F | 73.7 °F | 3.33 in. |
| May | 58.2 °F | 80.4 °F | 3.24 in. |
| June | 66.1 °F | 87.4 °F | 4.15 in. |
| July | 69.7 °F | 90.7 °F | 3.92 in. |
| August | 68.7 °F | 89.0 °F | 4.51 in. |
| September | 62.7 °F | 83.8 °F | 3.76 in. |
| October | 50.4 °F | 73.9 °F | 3.16 in. |
| November | 39.7 °F | 63.9 °F | 3.37 in. |
| December | 34.4 °F | 56.0 °F | 3.89 in. |
| Annual | 50.4 °F | 72.9 °F | 44.36 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 8a : 10°F to 15°F |
| Current Drought Conditions | Moderate Drought |
| Köppen Climate Classification | Cfa - Humid Subtropical Climate |