The glowing sky is set between dark hills and threatening storm clouds. At the bottom the exact date of 4 May 1821 and time of 5.30pm have been inscribed, in French, with the end of the brush. The artist must have started the study at sunrise, painting rapidly in order to seize the changing light.
The influential artist and teacher Pierre-Henri de Valenciennes recommended that no longer than half an hour should be spent when capturing such fluid light conditions. Although this sketch is unattributed the inscription implies that it is by a French artist.