how does the setting anticipate the events that happen?

A Separate Peace covers one year in time. The story is told from the perspective of our main character (Gene) when he is 30 years old and revisiting his boyhood school, and his reminiscing begins during the summer session of what I believe was his senior year. believe his senior year.

The weather plays a huge part in setting the mood and opens on a gloomy, stormy afternoon, cluing us in to the fact that we're not in for a bright and happy story.

The boys spent their summer in the sunshine having fun, but that quickly changes with the advent of the Fall session.

"...the Summer Session was over. It had been the school's first, but it was its one hundred and sixty-third Winter Session, and the forces reassembled for it scattered the easygoing summer spirit like so many fallen leaves." (Page 72)

In the end, Finny dies in the winter..... the season of cold.