out of a clear (blue) sky

out of the blue

Completely unexpectedly. She seemed so surprised by the news that it must have come out of the blue.
See also: blue, of, out

out of the blue

COMMON If something happens out of the blue, it happens unexpectedly. Then, out of the blue, a solicitor's letter arrived. Turner's resignation came out of the blue after his team's shock 5-0 defeat at Portsmouth. Can the disease really strike out of the blue? Note: This expression compares an unexpected event to a bolt of lightning from a blue sky. The expressions `out of a clear blue sky' and `a bolt from the blue' are based on a similar idea.
See also: blue, of, out

out of the blue

without warning; very unexpectedly. informal
This phrase refers to a blue (i.e. clear) sky, from which nothing unusual is expected.
See also: blue, of, out

out of the ˈblue

suddenly and unexpectedly: She had no idea that anything was wrong until he announced out of the blue that he wanted a divorce.
See also: blue, of, out

out of the blue

1. From an unexpected or unforeseen source: criticism that came out of the blue.
2. At a completely unexpected time: a long-unseen friend who appeared out of the blue.
See also: blue, of, out

out of a clear (blue) sky

Unexpectedly, suddenly. The image of something dropping from the sky was transferred to sudden or surprising events in the late nineteenth century. “He dropped upon me suddenly out of a clear sky,” wrote W. E. Norris (Marietta’s Marriage, 1897). It also was put simply as out of the blue, “the blue” having signified the sky (or the sea) since the seventeenth century. Oliver Wendell Holmes wrote in a letter in 1910, “I got an encouragement out of the blue . . . in the form of an honorary degree.”
See also: clear, of, out, sky