Flying a 500 in the Mojave desert, attempting to go over the mountains to a request for us. It was cloudy, some light rain, but no thunderstorms or anything that looked worse then I have seen numerous times before. First attempt at the direct route failed due to turbulance, so I went for my favorite canyon pass that I normally use for this type of situation. I just get into the canyon and find myself in a great updraft. VSI is pegged at over 3K' a minute and I have the collective on the floor. Now I am worried as that cloud above is getting really close, and fast, the helicopter is not really responding well, and about the only thing reliable on the instrument panel is the engine instruments. Was able to do a 180 and get out of it just as I was punching into the cloud deck. We went back to the hangar and set down for awhile after that.