Turbulence Is Predictable
If you fly over a mountain, you should expect some turbulence because there is mountain wind that blows right over the ridges. The wind generally creates up and downdrafts, which causes different wind currents going against each other, making it a bumpy ride for aircraft and passengers.
When flying through a jet stream, expect some turbulence due to the fast moving air currents. Depending on the speed of the jet stream, there may be minor or major turbulence.