What to wear in Boston in May?

Boston has a long winter, but the climate is changeable.

It is still very cold in March, and sometimes it snows heavily, so down jackets are needed.

April is still very cold, and it often rains, so you need ski clothes (there is a weird name in China called a jacket). I remember that there was a heavy snowfall on April 1st that was knee deep.

The weather in May can be changeable, sometimes very warm, sometimes very windy and cooling, generally requiring jackets and sweaters.