Jet streams occasionally produce turbulence, particularly at their boundaries. But often they are so smooth they suggest something like the opposite of their true dimensions. When it’s a little bumpy I remember that I am flying at 600 mph, in air that is moving at 200 mph, yet the plane is steadier than a car on a dirt road. Often the fastest winds are as smooth as glass.
Jet streams are actually quite smooth, esp when fast. It's entering and leaving that is turbulent.
Also earlier said that "jet" in jet stream has nothing to do with jets flying that high. It's actually more to do with the shape of the winds, narrow jets of wind.
