The poem follows a storm from start to finish, but it ends with a sting. Black clouds roll in, the rain pours, the wind picks up, and people hurry home for shelter. The speaker treats the storm as the end of a beautiful day. Then it passes: the sun shows through the clouds, the rain stops, the wind weakens, and people come back out.
Up to this point the poem is calm and observational, almost like a weather report. Then comes the turn: "But where are you?" Suddenly the speaker is looking for one particular person in the crowd, and the clearing sky doesn't bring relief. The storm may be a stand-in for loss, though the poem never says so directly.
The final line, "And the rain drops once again," works two ways. It could be real rain returning, or tears. Either way, the mood ends up lonely and sad. The weather clears, but the absence stays.