If we had snow days every time it snowed, we'd never have a summer vacation. A snow day in Canada was when freezing rain made the roads a complete sheet of ice and it fell between 2:00 am and 6:00 am. Those were days you didn't leave the house. Now it seems like on snow days you can drive any car, with any kind of tires, just about anywhere and you'll be fine.
There was one day growing up when they said it was too cold for school. It honestly wasn't very well thought out. They decided after we were at school that we should go back home. So at lunch time we all went home. It was great for bus students, but for those of us who lived in town we were walking home in really cold weather. I remember spitting and watching it freeze before it hit the ground. It was cold, but oddly enough, we all made it home safely and no fingers were lost to frostbite. I sort of reminded me of the kid who licked the flag pole in the Christmas Story.
In fact I think that should be the determining factor. Before a superintendent can cancel school for it being cold, he/she should do the tongue on a flag pole test outside.