Cloud-watching in early China is called yunqi, roughly "cloud vapours", and it was woven into a wider system of reading omens in the sky. In the Han era, which began in 206 BC, clouds, comets, haloes and rainbows were all signs that officials were expected to record and interpret.
One famous source is a set of silk manuscripts found in a tomb at Mawangdui, sealed in 168 BC. It includes a text on astronomy and weather signs illustrated with rows of small painted clouds, comets and vapours, each with a short note on its meaning. It is among the oldest surviving pictorial catalogues of its kind.
Another is a manuscript from the Dunhuang caves on the Silk Road, known as Zhan yunqi shu, which places cloud divination inside the same world of auspicious and disastrous signs. Han commentators also found hidden meanings in the clouds and thunder that appear in old poems such as the Shijing and the Chuci.
Auspicious clouds, xiangyun, left a different trail. Swirling cloud patterns became a beloved motif in Chinese art, carved on palaces and painted on silk as a sign of good fortune and heavenly favour. Scholars still debate the methods, the dates and how these traditions relate to those elsewhere. We should be careful not to assume a link with Babylon or Greece: there is no evidence for one.
