The weather changes very fast?

English as a Second Language English Vocabulary, Grammar and Idioms
1

Please tell me can we say the weather changes very [b]fast?

I wonder if the word “fast” is proper here

Thanks a lot.[/b]

2

I don’t think that the use of ‘fast’ is improper here. ‘Fast’ is an adverb meaning ‘quickly’. That may be the confusion I guess - ‘fast’ doesn’t sound like an adverb.