To answer this question, we need to understand subject-verb agreement in present perfect tense.
In the given sentence, the subject is "the weather" and the verb is "been". The correct form of the verb "been" in the present perfect tense depends on the subject.
Since "the weather" is singular, we need to use the singular form of the verb "been". The correct form is "has been".
Therefore, the correct answer is B) has. This option is correct because it agrees with the subject "the weather" in terms of number and tense.