That kind of turbulence can happen even at low levels if the wind is right, I was still a student and only just past Solo, I had entered left base for Runway 30 at NZOM this takes you into a small valley right up against the hills.
I entered a downdraft which took me from approx 900ft to 400 ft very quickly, having 10 deg flap i had throttle full open and the nose as high as i dared and i was still going down. had i not flown through it horizontally i would have arrived very quickly on the valley floor and probably would not have survived.
Also had a few friends get into Mountain wave over the southern alps having to call CHCH Info as they were throttled back to idle and going up at over 1000 fpm and busting airspace. ASI firmly in the yellow. I those cases it would only take some misjudged sharp control inputs to induce structural failure.
FK