In your fictional world, what season equates with our autumn? I can't see any way round having to have certain seasons. We need one for things to grow, to be in full bloom, to fade away, to seemingly die (until spring comes around again). But you could have in between seasons with their own names and times. What we call spring, summer, autumn and winter, you could rename. And you could use our own climates, weather patterns and seasonal changes as a model for what you create in fiction.
My maternal grandmother always hated autumn. She saw it as the time when everything died and she herself died in a September. I see autumn as what is necessary before spring comes again. How do your characters view the seasons and why? Is their outlook a pessimistic or pragmatic one? How does that trait affect their lives in general?