Hallettsville, Texas has a Humid Subtropical Climate climate (Köppen classification: Cfa). Average annual temperatures range from 14.6 °C (low) to 26.7 °C (high). Annual precipitation averages 982.5 Millimeters. Hallettsville is located in USDA Plant Hardiness Zone 9a. The growing season typically runs from the last frost around Feb. 11 - Feb. 20 through the first frost around Dec. 1 - Dec. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 5.1 °C | 17.4 °C | 70.87 mm |
| February | 7.2 °C | 19.3 °C | 54.86 mm |
| March | 10.9 °C | 22.9 °C | 71.63 mm |
| April | 14.3 °C | 26.3 °C | 71.88 mm |
| May | 18.8 °C | 29.9 °C | 116.59 mm |
| June | 22.2 °C | 33.1 °C | 110.49 mm |
| July | 22.8 °C | 34.6 °C | 57.15 mm |
| August | 22.8 °C | 35.4 °C | 81.79 mm |
| September | 20.2 °C | 32.6 °C | 95.5 mm |
| October | 15.1 °C | 28.3 °C | 104.14 mm |
| November | 9.8 °C | 22.6 °C | 80.52 mm |
| December | 5.9 °C | 18.4 °C | 67.06 mm |
| Annual | 14.6 °C | 26.7 °C | 982.48 mm |
| Average First Frost Date | Dec. 1 - Dec. 10 |
| Average Last Frost Date | Feb. 11 - Feb. 20 |
| Average Days With Frost | 10-20 Days |
| Plant Hardiness Zone | Zone 9a : -6.7°C to -3.9°C |
| Plant Hardiness Zone - 2012 | Zone 9a : -6.7°C to -3.9°C |
| Current Drought Conditions | Moderate Drought |
| Köppen Climate Classification | Cfa - Humid Subtropical Climate |