I've heard of cirrocumulus clouds, but...

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I’ve heard of cirrocumulus clouds, but don’t know how to recognize them. Can you explain?
Cirrocumulus clouds are loosely packed sheets of small, white cloud segments at altitudes of 18,000 to 20,000 feet or more. They form what some call a “mackerel sky,” resembling scales on a fish. The clouds may consist of ice crystals or water droplets or both. Their patchy appearance is caused by vertical air currents at the cloud level, indicating a lack of stability and a possible approaching storm.