Bom dia!  Which of these is good weather(=bom tempo)? a) Está a chover, b) Está a nevar c) O sol está a brilhar
Tip:  When you come across unknown words use the words you know to make a guess as to what it could be.  Use the context to help you too.  E.g. nebulosidade is not very far from nuvem(=cloud) so you could guess it has something to do with clouds