I googled it. Apparently, it's the opposite of a heat wave, though in America the term I hear more often is "cold spell"
I hear and say "cold snap" all the time! I guess it's more of a southern saying. You're right about the meaning. :)
ohhh, there are much much more different '한's in Korean than these two. Such as: 限, 恨, 漢, 汗, 韓, and handful of others of both Korean and Sinic origin