What do the black clouds symbolize in 'The Scarlet Ibis'?

The gathering black clouds at the end of the story symbolize and foreshadow imminent tragedy or death. Black is a universal literary symbol of death. Black clouds approaching a character symbolize the coming of death to that character. That coming death may be death of that character or someone close to that character. Here, the clouds approach both Doodle and his brother. Doodle dies. Doodle is close to the brother. Death came to both of them in one way or the other.