Will I be hot?
Will I be hot in San Jose in December?
Verdict
No — No, comfortable.
Highs cap at 57°F — no heat-management gear needed.
Day vs. night
Day
57°F
Cool
Sweater weather with the option to add a light shell.
Night
41°F
Cold
Cold enough that a hat and gloves become mandatory.
Why
San Jose in December averages highs of 57°F, lows of 41°F, 8 rainy days.
Temperature is comfortable across the day; pack for style and weather resistance, not heat management.