Watch: The Grand Canyon fills up with blanket of clouds in rare weather event

A rare weather phenomenon at the Grand Canyon had visitors looking out on a sea of thick clouds just below the rim on Thursday. The National Weather Service says it happens about once every several years. The fog that has been shrouding parts of northern Arizona is courtesy of recent rains. The Weather Service says the fog is able to stick around and built up in the Grand Canyon overnight when there is no wind. With an inversion, the clouds are forced down by warm air and unable to rise. The Grand Canyon is expected to gradually clear up in the coming days.