Will I be cold?
Will I be cold in Seattle in March?
Verdict
Yes — Yes, cold.
Lows drop to 40°F on average — noticeably cold, especially after sundown.
Day vs. night
Day
55°F
Cool
Sweater weather with the option to add a light shell.
Night
40°F
Cold
Cold enough that a hat and gloves become mandatory.
Why
Seattle in March averages highs of 55°F, lows of 40°F, 14 rainy days.
Plan for real winter kit — an insulated coat, warm hat, and gloves rather than a light jacket.