I too, have a strong relation between my moods and the changing of seasons. Even when I'm well balanced the increasing sunlight causes my sleep to be destroyed. Last night was the first night in weeks that I slept through the night, but even then I was awake in bed for a long while.
My worst manic episodes have occurred in the summer with a shift into a severe mixed episode during the fall and early winter, but that was two years ago. This year has been extremely mild.