Always you want to say It is in portuguese, you need say "está". You will be correct the most of the cases. To use "faz" in the case of the sensations, you need the gerundio, the same ing, and the to be: está fazendo frio. Literally: is doing/making cold. Cloudy can't be felt and is a weather's statement, so we can't use "faz", always "está". Please follow me and I can help you better.

"Faz nublado" it's wrong. Nublado is how is the sky It's cloudy! (Está = It's Cloudy= nublado).... but what we feel (hot, cold) we can say "FAZ" and "está". "Está frio/Está calor", and "faz frio/faz calor" but "está" we can use to speak about the situation. "Está calor, está frio, está nublado, está ensolarado, está quente, está úmido...."

You can't say 'faz nublado'. You can only say that to things that you feel Faz frio = está frio. See? Both tell you that you can feel the cold. Faz calor = I'm also expressing I feel the heat. The only exception to this "rule" (it's pretty general, there are going to be exceptions but that seemed to work for most foreigners so far) is Faz sol... which means "it's sunny" or sometimes "it's hot"

It is cold = Está frio - Use to 'faz frio' too. It is cloudy = Está nublado