Thursday - October = Scraping Windows

I had ice on my windshield this morning. I had to scrape it. I was unhappy about that. I wonder what time you have to leave by to not have your windshield ice up. There has to be a specific thing that causes it because I've left at midnight and not had to scrape the windshield. Maybe there is a windshield icing fairy that operates like the tooth fairy and only comes when you're asleep. If that's the case, I'm never going to sleep again!