The aircraft registered peak acceleration values of +9 and -4 "g",
Megan,
When you are not expecting it, that would be staggering, even for a fighter pilot!
ICT_SLB,
Lee waves are very common all over the western US and Canada, when the wind direction, topography and air masses are conducive to their formation. They routinely extend into the stratosphere. The Canadian glider altitude record is 34,400' (Cowley, AB) and the US record is 49,000' (California City CA). At altitude, the wave flow is laminar and very smooth. Turbulence is unusual. The risk of turbulence increases at lower levels, at or near the mountain tops and so it is typically during climb and descent that commercial aircraft encounter.
However, the turbulence, while uncomfortable for the passengers, hardly ever reaches the "severe" classification. I've only experienced severe turbulence on a couple of flights, for very brief periods.
The turbulence associated with the Mt. Fuji accident was extreme. It would certainly make me think twice about flying downwind of a volcano.
I live in Calgary, about 50 nm downwind of the Rockies. On "blue wave" days, with no lenticulars, it is quite common to see the contrails of E-W jets appearing and disappearing as they fly through the peaks and troughs of high altitude waves.