From this article in Popular Mechanics they explain,
“These days, airlines and air traffic controllers are very, very good at routing planes around the clouds and thunderstorms that bring heavy turbulence, because these weather events show up in neon colors on any radar sweep. What’s harder to avoid is “clear-air turbulence”—a form of wind shear invisible to radar that occurs when layers of air of different density swarm around each other at extremely variable rates of speed.”
The result can be horrifying as seen in the following video.
One possible solution is the use of lidar to detect the density of air in front of it by how much light is reflected back. If a pilot suddenly saw a patch of air with wildly varying densities, they could possible dive or climb to avoid the rough patch, or at least be able to have everyone strap in before the shaking starts.
So far none of the airlines are using this approach.