Wow... the only time I've heard of school closing early is if a fluke storm blows in and ICE threatens... we don't usually get snow, we get ice, and that's a booger to drive in... but even that would be a rare thing to do because so many kids would be left unsupervised/without a ride... between 600-700 kids just in the nearest elementary... that's a lot of calls to make...
Normally if it gets really hot, at least 95 (or too cold, though I don't know what that temp is) then they keep the kids in, no outdoor recess... but they don't cancel school.