wind chills have nothing to do with closing school, its the actual air temperature that does- which isnt going to be -17 unless you live in manitoba canada etc.
As to the cold, thats not cold enough- you need below zero readings for 2-3 days in a row for a day off given the busses will start just fine if its just a day or two as expected, it takes 3 or so days before the fuel lines begin to freeze and then not start which would be the primary reason to call school off.