It is in a one-part form.

a (measures 1-8) + a1 (measures 9-16) + Coda (measures 17-20)

The key is G major. The theme has a two-part structure: a motif composed of ascending eighth notes containing non-chord tones, and in contrast, a motif of chords with little movement in measures 3-4 (measures 1-4). This progresses with subtle sonic variations, and the way the harmony changes richly in color, centered around the IV chord as a secondary harmony and extending to added-sixth chords and 11th chords, likely depicts, as the title suggests, the way clouds drift and change in various ways.