Three short lines, and almost nothing in them, which is exactly the point. The speaker names fog, then addresses a person, "You again," then names fog once more. The word "again" appears twice, so we understand that both the weather and this person keep coming back. The poem never says who "you" is or what happened between them, so we have to guess from the way it sounds.
The tone reads as weary rather than angry or joyful. "You again" could be said with a sigh, a flinch, or a reluctant kind of recognition. Placing "you" between two mentions of fog suggests the person arrives the way fog does: unasked, blurry, hard to see past. The title, "Closure," adds an ironic edge, since nothing here feels finished. If anything, the pattern is repeating. The mood is hazy, stuck, and quietly heavy, and the stark white space around the words makes the silence feel as thick as the fog itself.