Asking a Boy to Winter Formal?

I've liked this guy for a really long time and we have had a couple classes together over the years, but we don't really get the chance to talk that much. We've had short conversations a couple times and now he always says hi to me in the halls (no class this year together). I wanna ask him to winter formal, but it's hard because we hang out with a completly different group of people. How should I ask him without making him feel awkward?