Kanji for Cloud

雲 covers the whole of it: cloud in every sense, read kumo alone and un in compounds. In compound words the kun reading voices to -gumo — 雨雲 amagumo, rain cloud; 入道雲 nyūdōgumo, the towering summer thundercloud.

The character reaches past weather. 雲海 is a sea of clouds seen from above a mountain, 暗雲 the dark clouds of a looming crisis, and 雲隠れ means to vanish, literally to hide in the clouds. Height and distance come with it, and with them a sense of the remote and the unreachable.

Watch out for 曇. It is built on 雲 but means overcast — the weather condition rather than the object. 曇り is what a forecast says; 雲 is the cloud you can point at. There is no second character competing for this meaning, which makes 雲 an unusually simple choice.