Formation of altocumulus duplicatus clouds formed primarily due to a very steep lapse rates in the upper levels of the atmosphere due to the inflow of very hot air at altitude but which was cooled at the very surface due to a cooler sea. This information is depicted by the weather sounding on the first thumbnail. The hot air was due to an upper-level trough pushing cold air southwards towards Northwest Africa which encouraged the North African anticyclone to bounce towards the Mediterranean. A heat low was present over Northern Africa.