Our school didn’t cancel classes the Monday after Thanksgiving, despite the (fairly minor) storm. They sent out an email informing the faculty that many students were not able to return because of cancelled flights, etc. and asking that we have mercy on students who were not able to get back in time. The general tendency is to close the school if things are, or are getting, drastic. Since that happens as much as once a semester, they need to be judicious about it.