A quiet moment in a house: sunlight pushes through a snow squall and the glass of a back door, and the speaker, standing there, says plainly, "I miss you." There's no explanation of who the "you" is or where they've gone. The poem simply lets the absence sit in the room.
What makes it work is how small and physical everything is. The speaker doesn't describe heartbreak. Instead we get cold knees and the little popping noises they make on the stairs. Those details suggest a body feeling its age, and a person moving through the house alone, noticing sounds that someone else might once have heard too. The weather adds to this: sun and snow together feel mixed, bright but cold, much like the feeling of longing itself.
The mood is gentle, wistful, and a little weary. The title, "Blues," fits, but the sadness is understated, tucked into ordinary things rather than announced.