Answer :
The storm seems to be over—no, the sky is darkening again. shows the correct use of a dash or dashes.
Dashes are versatile punctuation marks often referred to as the "super comma." They are used to set apart or emphasize content within or after the dash. In this context, the dash emphasizes a change in thought or emotion in the sentence.
For example: The storm seemed over—no, the sky is growing darker once more. This structure allows the interruption to be clear and impactful.
