Asking the Girl Out (college)

I am a sophomore in college. There is a girl that I really like, and it is pretty obvious that the feelings are mutual. We've been hanging out casually a lot recently, and when we're not together, we're usually texting each other. I know I'm going to ask her out, that's not the problem. The problem is that the Fall 2013 semester at my college is going to end in less than 2 weeks, and then I'm not going to see her for all of Winter Break (6 weeks). Should I ask her out now and start a relationship when pretty soon I'm not going be able to see her for 6 weeks, or should I wait the 8 weeks until the beginning of the Spring 2014 semester to ask her out?

I have this fear that attraction has an expiration date, and if I don't take advantage of this opportunity, it will go away. I really like this girl, so I want to ask her out ASAP, but I have this nagging feeling that the apartness for a month and a half could have a weird affect on the beginning of our relationship. Am I thinking about this too much when it's not really a big deal, or are my concerns relatively founded?

What would you guys do in my situation?

Thanks!