San Marcos, Texas has a Humid Subtropical Climate climate (Köppen classification: Cfa). Average annual temperatures range from 14.1 °C (low) to 26.5 °C (high). Annual precipitation averages 905.8 Millimeters. San Marcos 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 Nov. 21 - Nov. 30.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 4.1 °C | 16.8 °C | 57.91 mm |
| February | 6.1 °C | 19 °C | 45.72 mm |
| March | 9.9 °C | 22.6 °C | 74.68 mm |
| April | 13.7 °C | 26.3 °C | 73.66 mm |
| May | 18.4 °C | 29.9 °C | 118.11 mm |
| June | 21.9 °C | 33.2 °C | 85.34 mm |
| July | 22.8 °C | 35 °C | 53.34 mm |
| August | 22.9 °C | 35.8 °C | 67.06 mm |
| September | 20 °C | 32.4 °C | 90.93 mm |
| October | 14.7 °C | 27.8 °C | 106.43 mm |
| November | 9.1 °C | 21.8 °C | 70.1 mm |
| December | 5 °C | 17.6 °C | 62.48 mm |
| Annual | 14.1 °C | 26.5 °C | 905.76 mm |
| Average First Frost Date | Nov. 21 - Nov. 30 |
| 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 8b : -9.4°C to -6.7°C |
| Current Drought Conditions | Moderate Drought |
| Köppen Climate Classification | Cfa - Humid Subtropical Climate |