Is turbulence detectable in advance?

[Nik]

Modern airplanes boast to have an advanced navigation and meteorology systems, however from my experience of hundreds of flights the early warning is rare. It's rather first you feel turbulence and then the crew switches fasten your seat belt sign on.
Is turbulence (especially 'clear air') something that can be detected?

[Ian]

Nik, I have been on flights where there has been reasonable warning of turbulence, although this might be because they were crossing zones where turbulence was fairly normal. They say they can detect it, but it may be that it works only for certain sorts of turbulence.

[Nik]

Or they hear reports of other pilots in the area through the tower.. As then there are also instances when they do warn, while nothing happens afterwards