Formation of cirrus vertebratus similar to fish bones and some spissatus (thick cirrus) due to an easterly moving low pressure system near the Bay of Biscay along with its frontal system as can be evidenced in the satellite cloud map on the 2nd thumbnail (high clouds were not visible but the cloud system was) and confirmed by the surface pressure chart on the 1st thumbnail. The 3rd thumbnail indicated lots of moisture at upper levels along with wind whereby air flowing parallel to the cloud line created its ribs when it was rising and the space between the ribs when it was descending.