Nimbostratus painting the sky

This photo was taken in Valencia (Spain) during a storm formation.
Nimbostratus are described as a grey cloud cover with a veiled appearance due to the precipitation (liquid or solid) holded within them. They are formed when a large layer of relatively warm and humid air ascend above a cold air mass. Together with the Altostratus, it is the core of a warm front.
The aim of the photography was to freeze the moment in which the clouds covered the sky in a way that seemed it was painted.