Thank you all,I´ve learned a new word!

Scud are just low clouds similar to broken fog but above ground level.  We used to fly on the coast close to the ground in this type of weather. We called it scud running. 

Scudding clouds are moving clouds. Scudding means moving along swiftly.

The swiftly moving clouds are called scudding clouds usually followed by gale. A gale is a strong wind.