This is the 19012th most frequent Korean word.
아니었지만
"Was not, but..."
In this sentence, "아니었지만" connects two clauses, indicating that the preceding clause is negated while introducing the following contrasting clause.
그것은 진실이 아니었지만, 사람들이 믿고 있었어요.
It wasn't true, but people believed it.
Here, "아니었지만" negates the subject's profession and contrasts it with their actions of attempting to heal.
그는 의사가 아니었지만 고쳐보려고 노력했어요.
He wasn't a doctor, but he tried to fix it.
In this context, "아니었지만" expresses the negation of the weather's quality followed by the continuation of their plans.