WHEN THE PLT TOOK OFF FROM A MOUNTAINOUS SKI AREA, LIGHT TO MODERATE SNOW WAS FALLING & THE WINDS WERE COMING UP THE VALLEY AT 5 TO 10 KTS. DURING THE FLT, HE ENCOUNTERED AN ESTIMATED 35 KT UPSLOPE WIND AS HE WAS PROCEEDING ON THE UPWIND SIDE OF A RIDGE AT AN ELEVATION OF ABOUT 12700 FT. WITH THE UPDRAFT, HE WAS ABLE TO REDUCE POWER. THE HORIZON WAS NOT VISIBLE BUT HE COULD SEE THE MOUNTAIN TO HIS LEFT REAR AREA. JUST PRIOR TO THE ACCIDENT, THE ACFT WAS TRAVELING AT ABOUT 40 KTS AT 100 TO 150 FT AGL. THE PLT STATED THAT WHILE HE WAS STILL IN AN UPDRAFT WITH REDUCED POWER, HE LOOKED BACK, NO MORE THAN 3 TO 5 SEC. AS HE LOOKED FORWARD AGAIN. HE ENCOUNTERED A WIND SHIFT WHICH PUT HIM IN A DOWNWIND, LOW POWER SITUATION. FEELING THERE WAS INSUFFICIENT SPACE TO TURN DOWNHILL, HE TURNED UPHILL, ADDED POWER & FLARED. THE HELICOPTER TOUCHED DOWN HARD ON STEEP TERRAIN AT ABOUT 12500 FT. THEN BECAME AIRBORNE AGAIN. IT IMPACTED AGAIN AFTER DROPPING 15 TO 25 FT & CAME TO REST. THE T/R & T/R GEAR BOX SEPARATED DURING THE SEQUENCE.