Not to mention turbulence caused by the wind currents through mountains, especially if its in a valley as this very much appears to be. The mountains form a wind tunnel effect which can play havoc with aircrafts of any kind.
not necessarily. certainly the maneuver would be practiced, but for the most part, the training is held in ideal conditions. that chopper needs to be set down enough that it wont bounce around, and yet it cant cave in the roof. The practice maneuvers are done on concrete and steel.
Also don't forget that if you don't maintain enough force the helicopter could break the roof.