The speaker watches how winter changes a landscape and, with it, how we see. Seasons alter what's on the horizon: what looked like a mountain in summer turns out to be a hill once the leaves fall, and a sudden "influx of sky" opens up from the front porch. Then snow arrives, and the poem slows down to watch it settle, "lightness piling up" between the trees.
The imagery grows strange and quietly beautiful. Snow becomes a "colony of the clouds," pale and "puritanical," while the bare trunks turn into an "absent crowd / dreaming / together / underground." The tone is hushed and attentive, with a gentle wonder rather than any sadness about winter. The ending brings a small surprise: after sleeping, the speaker looks again and sees a squirrel walking upside-down along a limb. It's a playful last note, suggesting that looking carefully, and looking again, keeps the world fresh and a little odd.