Such high-level clouds are made of many tiny millions of ice crystals that as they look in the photo are scattered all over the sky due to strong 150kmh jet stream blowing over the high-level clouds. Such jet stream create these specific type of clouds in the presence of moisture at high levels as per second thumbnail of the weather sounding. The first thumbnail shows a wider view of the cloud cover having part interlaced formation and the rest of its ice crystals splattered all around the place whilst the third thumbnail show a strong jet stream blowing over Malta from North America itself. The fourth thumbnail show upper level positive temperature vorticity hence rising air and the fifth thumbnail shows a complex area of low pressure that was covering most of Europe at the time. In fact, upper-level thunderstorms had occured early on that day. Hence these clouds were actually the last available water vapour from the bad weather system which was then followed by clear skies.