I wasn’t there and didn’t experience this event, but I have in the past.
I would suggest that this was a manifestation of rotors. The strength of the wind is not the issue here, but the presence of a deep, stable layer with little vertical shear throughout the troposphere.
In such circumstances, when the wind is incident on a barrier such as a mountain range, longitudinal harmonic vortices called rotors can form just like from the reed in an organ pipe. The question of lenticular cloud is germane because the presence of such clouds is a sign of the possibility of rotors.
Stacked lenticularis, particularly when in regularly spaced groups is a harbinger of the presence of rotors and the possibility of severe turbulence. Also the clouds produce severe icing as a result of forced uplifting of saturated air. They should be avoided if possible. The rotors will be between and below the lenticularis as they generally form in the 'troughs' of the lee wave. Conversely, the clouds mark the peaks of the wave.
Such phenomena may not be forecast on significant weather charts, since no winds below 80 kts are shown, and their incidence may be temporary and sporadic. The art of the professional airman is to recognise the warning signs, and be prepared:
- A deep stable layer with little shear up to the trop. Check the wind charts.
- An incidence over a lateral barrier of less than about 30˚
- A warm moist airmass
If you’re not fortunate enough to avoid it, keep the attitude as constant as you can, ditch the autothrust and make smooth adjustments with power, remember you may be close to the surge boundary, tolerate the variations in speed and altitude within reason.
Make a ‘securité’ broadcast on the frequency in use and 121.5 giving your position, level and heading.
You won’t be able to maintain RVSM, and the call to ATC is MAYDAY if you can’t achieve a sympathetic reclearance.