To add to what Sevenstrokeroll said about flying in mountainous areas, once convection really gets going, you can get some impressive sinking air without any storms or even clouds. It wouldn't be at all unusual to find an area going down at 1,000fpm plus that might take some time to get out of.
I've flown a fair bit in Nevada and at times the ground appears to be porous if you're in the wrong place! The mountains in Idaho probably behave in much the same manner. The middle of the afternoon is not the ideal time to go aviating in a marginally-performing aircraft...