BluSdUp : good comments cannot agree more with you , I know the power of waves as I fly gliders too.
Rorobskye :
However this accident seems to be a VMC into IMC/CFIT than a mountain wave issue.
Yes, but could be both, a medium size cumulus hiding the top of the hill, you are planning to go on top of both but the downdraft catch you and force you in, you see the ground on the other side, tempted to let it go into the cloud for 10- 15 sec max ? except this time the top of the hill is in the cloud. , but speculating , could be anything else, Reminds me a bit of the Santa Maria Independent air 707 ( 1989 , check google if interested) hitting the highest tree on top of the only obstacle in the area for hundreds of miles, in clear blue sky .. except for the cumulus on top of the old volcano..