mackerel sky

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A sky covered with many small cirrocumulus or altocumulus clouds, resembling the markings found on a mackerel.

from The Century Dictionary.

• noun A sky in which the clouds have the form called cirro-cumulus—that is, are broken into fleecy masses three, four, or more times as long as they are wide, and arranged in parallel groups. Also called mackerel-back sky.

from the GNU version of the Collaborative International Dictionary of English.

• noun A sky filled with rows of cirrocumulus or small altocumulus clouds.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun a sky filled with a regular pattern of altocumulus clouds somewhat resembling the skin of a mackerel.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a sky filled with rows of cirrocumulus or small altocumulus clouds