severe turbulence can also come from mountain wave to many thousand of feet above the Mountain range altitude
Wave is also paradoxically super smooth when in the lift zone; I once flew from the Peak District past Nottingham hopping from one wave bar to the next, climbing in each in my little unpowered hang glider in such smoothness in a clear evening sky that it felt I was hanging from some invisible hook, and next day i noticed the left side of my face was noticbly more sun burned than the right side, from the steady oritentation whilst climbing. And yes, under the wave it is not a nice place to be on any small craft.