Why "está nublado" instead of "está nublando"?
"nublar" is a verb meaning "to cloud over", so why not use the gerund, the same as in "está nevando" (it's snowing)?
4 Answers
In English you probably wouldn't say "It is clouding" even though it is grammatically correct, but you would say "It is clouding over."
Is there a rule for this? No, it's just the way it is.
Nublado, -a is an adjective made from the past particple of nublar, it means cloudy, and that's what you use to say "It's cloudy." There are many other adjectives made from the past participle of verbs, in fact most past particples can be used as adjectives: cerrado, abierto, etc.
By the way I think nublar (meaning to get cloudy) is usually used reflexively -
Se nubla ahorita, que lástima!
When it gets to the point that it is clouding over, it is already clouded over.
Está nublando and está nublado mean seperate things.
está nublado is - it is cloudy (nublado is an adjective)
está nublando - it is clouding over (progressive present tense)
if you want to use the gerund you can say "Se esta nublando"
other ways to say it will be "Esta nublado", "Ya se nubló"