How do they know?

We got dumped on by a mini snow storm last night and as a result the kids have a snow day today. Since this all happened while they were sleeping, how on earth do they know before they even wake up? On usual school days I can barely shoehorn them out of bed in time to get to school. But today, like a weekend, they've popped out of bed bright-eyed and bushy-tailed and a full hour before they would had they had to go to school. Is it some trace mineral or element in their system that leaches out before adulthood that lets them be so attuned to this school-free day? I mean seriously! We could have slept in, caught up on all our lost sleep, but no we're up to greet the sun and raring to go with nothing to do. Maybe I can convince them to make a sleeping snowman while I supervise through my eyelids from the horizontal position. ::yawn::