A video shared by the Grand Canyon National Parks Service shows clouds pulsating inside one of the seven natural wonders of the world. This rare meteorological phenomenon is called a cloud inversion, and it only occurs here once every few years. It happens when cold air down in the canyon meets warm air from above. The result is clouds looking more like waves against the walls of the canyon. According to weather reports last week, temperatures during the day were averaging close to 69 degrees Fahrenheit and dropping to an average of 30 degrees at night.