Will I be hot?
Will I be hot in San Antonio in December?
Verdict
No — No, comfortable.
Highs cap at 63°F — no heat-management gear needed.
Day vs. night
Day
63°F
Comfortable
A T-shirt and a light overshirt is enough.
Night
41°F
Cold
Cold enough that a hat and gloves become mandatory.
Why
San Antonio in December averages highs of 63°F, lows of 41°F, 7 rainy days.
Temperature is comfortable across the day; pack for style and weather resistance, not heat management.