A record-breaking heat wave is threatening more than 24-million Americans.  Communities from Texas, to the Northern Plains, to New England are under a heat advisory and at least six states hit record highs Monday.  A heat emergency is out for Boston, where temperatures climbed above 90 for a third straight day.  At least 15 public schools in Minneapolis are moving to remote learning from today through Thursday.  Heat and humidity are generating scattered severe thunderstorms from Alabama to Texas and more than 100 homes were flooded outside Houston.