The very first photo, taken from the chopper seems to indicate that the roof was like that because of the crash.
I know what you mean Pace, I've had 1500 fpm decents full power (trying to climb) with the stall warner chirping while flying in the mountains, followed by 1500 fpm climbs with power at idle very shortly after. It was pretty windy though - 30kt plus according to Garmin. I remember reading an accident report of a glider / tug combo which encountered moutain waves causing the tug to break up and the glider to experience 14g (and land safely).
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.
Wouldn't Avgas have the effect of melting the snow had the tanks ruptured with a lot of fuel onboard, or would it evaporate quickly. I can't see any obvious signs of fuel spill in any of the photos.
I am only speculating because I am keen to know why this happened so that it doesn't happen to me.