This is one of the earliest of a number of Constable’s 1821 cloud studies in which he included a margin of land or treetops along the bottom of the image. Here he depicted the sunlight catching the tops of the small cumulus clouds, using long, sweeping brushstrokes in the upper right to express the movement of the clouds in the wind. There is good agreement between Constable’s inscription and the weather records for the London area on that day, which suggest it was a fine day with some cloud, warm temperatures and high humidity. The streets of small cumulus clouds are typical of a light westerly wind (Thornes 1999, pp. 224–25).

On 17 October 1820 Constable painted his first known dated oil sketch at Hampstead in which he recorded weather effects, Sketch at Hampstead, stormy sunset (Victoria and Albert Museum, London).He continued  his systematic study of changing skies over the following two years.  On 23 October 1821 he wrote to John Fisher:

I have done a good deal of skying– I am determined to conquer all difficulties and that most arduous one among the rest, & now talking of skies – …That Landscape painter who does not make his skies a very material part of his composition – neglects to avail himself of one of his greatest aids.Sir Joshua Reynolds, speaking of the ‘Landscape’ of Titian& Salvator & Claude– says ‘Even their skies seem to sympathise with the Subject’ …It will be difficult to name a class of Landscape,in which the sky is  not the‘key note’ – the standard of ‘Scale’, and the chief ‘Organ of sentiment’… The sky is the ‘source of light’ in nature – and governs every thing. Even our common observations on the weather of every day, are suggested by them but it does not occur to us (Beckett VI, pp. 76–77).

Constable considered that: ‘Nature is never seen, in this climate at least, to greater perfection than at about nine o’clock in the mornings of July and August, when the sun has gained sufficient strength to give splendour to the landscape, :still gemmed with the morning dew”’, without its oppressive heat; and it is still more delightful if vegetation has been refreshed with a shower during the night’ (Beckett, Discourses, p. 17).Although he painted this sketch a little later in the day – between 10 and 11 am, and in early September – Constable has captured the freshness of the morning sky.

As with this work, Constable painted many of his cloud studies in about an hour. His reference here to ‘rain in the night following’ indicates that the inscription was added a day or so after ‘Sepr 11’, and that in making these cloud studies he was not only interested in weather conditions at the time of painting, but also the weather before and after that time.  He was interested in changing conditions, in fluctuating moments, shifting effects of light and shade – and how these impacted on a landscape.