Hi, Kim. I'm not "exactly" sure what you're asking, honey. But if it's do you EVER make the seasons plural, the only time I would know of is, for instance one might say, "The winters of 2001 & 2002 were particularly harsh." But as far as the example you used, you would always use it in the singular. "I go skiing in winter," or I go skiing every winter." I don't know if that's what you were asking or not, sweetie.