If all was well before you stored it, you may just need a little lube at all the friction points. I would do that before adjusting anything. A little WD-40 may do the trick. Check for spider webs or any other gunk that may have built up.
You have cold grease my friend! The cure will come with the warmer weather. The correct way to fix it, if you can't live with it, would be to take the shifter off and apart, clean and regrease. Warning, the shifter is like a jigsaw puzzle when you take it apart.
