Timelapse footage of a band of cirrus clouds marking the position of the jet stream. Ice crystals are seen to fall from the band. The jet stream is a river of fast-flowing air that flows eastwards around the Earth at high altitudes. They typically form at the boundary between two of the large-scale atmospheric cells that move air around the atmosphere, generally at latitudes of 30 and 60 degrees north or south. However they may develop significant kinks and meanders called Rossby waves, which can divert them to higher or lower latitudes. Filmed in the USA on a winter afternoon.