The jet stream is a river of winds in the upper atmosphere that weaves around the north and south poles. "The purpose of the jet stream is to balance and distribute heat in the atmosphere. Near the equator, it's much warmer. The warm air rises. Near the North Pole, it is much colder. The cold air sinks," says Matthew Cappucci, a meteorologist at MyRadar. Cappucci breaks down the role jet streams play in weather systems. | PBS NewsHour