December in San Marcos averages a daily high of 18.2°C with nights around 5.2°C. Expect roughly 7.1 wet days totalling 47.1mm. Comfortable conditions for being outdoors all day.
Across the year, the best time to visit San Marcos is February–April.
Based on SAN MARCOS, TX US (0.8km), 1995–2024. 30 years of December data.