Will I be hot?
Will I be hot in Mexico City in December?
Verdict
No — No, comfortable.
Highs cap at 71°F — no heat-management gear needed.
Day vs. night
Day
71°F
Comfortable
A T-shirt and a light overshirt is enough.
Night
45°F
Cold
Cold enough that a hat and gloves become mandatory.
Why
Mexico City in December averages highs of 71°F, lows of 45°F, 3 rainy days.
Temperature is comfortable across the day; pack for style and weather resistance, not heat management.
The day-to-night temperature swing is 26°F, which is the real story here — the average number hides how different midday and midnight feel.