These clouds were seen in mid-afternoon and could have been remnants from high-based cumulonimbus clouds that passed in the vicinity of the area. As can be seen in the weather sounding of the first thumbnail, the cloud`s temperature of at least -30C with a base of at least 8.3km, the cloud`s droplets were definitely composed of ice cyrstals. A very strong overhead jet stream, created the fibratus effect on the cloud cover meaning that they were changing shape rapidly and the wind`s affect on the cloud made it look as if the trails of the cloud were curling up. The jet stream wind is shown in the second thumbnail.