A patch or layer of cloud consisting of tiny individual cloudlets at high-level is called cirrocumulus. The cloudlets may make a regular dappled or rippled pattern. Sometimes they look like the scales on a fish - a "mackerel" sky that may mean that unsettled weather is on its way. Like all high-level clouds, cirrocumulus is made of ice crystals. It forms when cirrus or cirrostratus is warmed gently from below. This causes air to rise and sink inside the cloud. Some of the ice crystals change into water vapor, and gaps appear. It can be difficult to tell cirrocumulus from altocumulus. Cirrocumulus has no shading (which altocumulus usually has), and because it is so much higher, the cloudlets of cirrocumulus are much smaller than those of altocumulus.
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