Not on display
It is unclear whether the drawing represents a single sky with upper and lower bands of cloud, or two successive views of the same formation. Towards the centre left is a small disk, presumably representing the sun or moon, with a wavy vertical line underneath, below what may be the horizon at the bottom left, perhaps indicating a reflection in water. The drawing continues across folio 22 recto (D40852, a torn stub) and folio 23 recto (D12154; CLIV a 22).
As set out under folio 7 verso (D12134), there are nearly thirty pages of cloud studies in this sketchbook, some annotated with colours, as here, and other observations.