Following forum member 744rules, they said something on TV
about this, and this phenomen happens when warm clouds go upstairs, and come in collission with cold clouds coming downstairs.
Anyway, still very strange...
Yyz717 - no idea if the temperature decreased suddenly. I quickly went back inside, it was raining too heavy.
Mbmbos: it was indeed a very heavy storm. There even was a green shine in the dark clouds on a sudden moment which means heavy thunderstorms.
If someone has more information, please post it.