Out of the blue

The phrase, out of the blue, means that something happened suddenly that was totally unexpected and without warning. It could be that it just happened unexpectedly. It could also be that someone said something that was off the subject of what was being talked about or didn't have any relation to anything that anybody else was saying. I If someone does something unexpected and without any warning, you could say that he did it "out of the blue." Someone you haven't seen for a while can suddenly show up "out of the blue." John: What happened to you? I haven't seen you for a while. Dan: I was transferred to another project. John: What? I thought you were working on Project X. Dan: I was. The project manager showed up one day, out of the blue, and told me I was being reassigned to Project A. John: Well, I guess they needed a good man for the job. This expression seems to refer to it starting to rain unexpectedly, even though the sky was blue. There was no warning like gray clouds. It just happened "out of the blue." An older form of this expression is, "out of the clear blue sky," though this is not used much any more.