But I still don't see how on an apparently good weather day (good enough for the chopper to by flying there) you could get such dangerous down drafts above the ridge (they must have been above it to hit it with that much impact). If you had 20+ kts of wind at the top of these mountains there would be significant wind blown snow in the lee I should imagine and I'd have though that would have been a good clue to the pilot to stay high.
To say this you can't have done much flying around mountains.
