We saw a blue sky for the first time in weeks, perhaps a good omen.
I'm not sure if the phrase in bold is called a reduced relative clause in grammar. Actually it modifies the whole sentence that comes before it.
We saw a blue sky for the first time in weeks, perhaps a good omen.
I'm not sure if the phrase in bold is called a reduced relative clause in grammar. Actually it modifies the whole sentence that comes before it.
It is a reduced relative clause and it is true that this relative modifies the whole previous clause. Although Cambridge seems to indicate that this use is more often encountered in spoken language, it is often used in written formal language too:
Some relative clauses refer to a whole clause, a whole sentence, or a longer stretch of language. We always use which to introduce these clauses. We often use these clauses in informal speaking to express an opinion or evaluation.
- I think the other thing that was really good about it as well was that [everybody worked really hard and helped tidy up at the end], which I hadn’t expected at all. (In this example, the which clause modifies the italicised clause).
So your example could be re-written with the omitted words:
We saw a blue sky for the first time in weeks, [which was] perhaps a good omen.
here again, the which clause modifies the italicised clause.
Edit: I am ready to accept I am wrong and learn something new. I just wish people made the effort to also give the right answer, which they must know since they downvoted. When someone gives a correct answer, I will gladly delete mine.