I'm not familiar with the Ozark Highlands Trail specifically. However, having done almost all of my hiking in the south (Texas and southern Arkansas), I'll mirror what Slowfoot said about the weather being unpredictable. The good thing about it being alternately cold and hot is that the snow, if there ever is any, doesn't have a chance to stick around and build up like it does in more northerly states. If you're used to snow and ice, I wouldn't think you'd have a problem at all. I actually prefer to do my backpacking in winter and early spring, because I don't like being out in the heat (and I don't like the mosquitoes). Somehow, it seems like it still ends up being 80 in December when I get out.

You might also consider the Ouachita Trail.

EDIT: Sorry for resurrecting this thread; for some reason it was showing up as unread for me. I'd already posted my reply when I noticed the date on it.