Reuters reports a heat wave has blanketed about a third of the population of the United States in recent day.br But the National Weather Service says the heat is due to break on Monday, in a burst of thunderstorms brought on by a cold front.br On Saturday, new one-day temperature records were recorded in at least half a dozen places.br Officials implored everyone to stay inside as much as possible and be alert for the signs of heat stroke.br In New York, the streets were unusually empty.