Formation of lumps of cotton wool clouds ahead of an approaching cold front which is indicated on the third thumbnail. Well before the approach of the cold front itself, the present air mass was forced to rise over the approaching colder air leading to such cloud formation despite the atmosphere being relatively stable higher up. In this case, the bad weather clouds evaporated just after having reached the Maltese Islands due to general stability in the area leaving only some drizzle. Normally, such cloud formation is associated with a brewing thunderstorm.