 for a fifth straight day. According to the National Weather Service, the city hit 119 degrees Tuesday and reached 120 degrees Sunday for the first time in history. A rep for the National Weather Service calls this the most extreme heat wave in the history of record-keeping in Las Vegas since 1937. More than 142 million people across the U.S. are under heat alerts, many out west, where the duration of the heat has been a major concern.