According to the accident pilot, after transferring a patient from Klamath Falls, Oregon to Bend, Oregon, he received a request from his dispatch to collect a patient in Christmas Valley, Oregon. He reviewed weather information from stations surrounding the destination as there was no local weather reporting facility at the destination. The pilot recalled that the expected winds were from the northwest at 15-20 kts sustained, and gusting to 30 kts, but were acceptable for the flight. After a preflight inspection he departed on the accident flight with three flight crewmembers. They did not experience any significant weather while enroute to their destination and the helicopter was operating within its normal limitations. The pilot approached the airport by entering the airport traffic pattern from the north for a landing to the west as the winds were from the west/northwest. He recalled that the windspeeds at the time of arrival were approximately 15-20 kts and gusting between 25-30 kts. After he became established on final approach he sidestepped and approached a parallel taxiway. He slowly taxied while looking for the air ambulance they were scheduled to meet. The pilot reported that he was monitoring the windsock during this time, but observed the helicopter handling well with no indication of winds that would exceed the helicopter’s limitations at the time. Once he identified the landing site he lined the helicopter with the landing pad and began a descent while noting several structures nearby that were providing protection from the wind. At this point he performed a right pedal turn from about 3 ft above ground level to position the left door towards the ambulance for the pickup, consistent with the operator’s protocol. The pedal turn went smoothly; however, as the helicopter touched down it was forced forward rapidly. The pilot reacted by increasing collective and applying aft cyclic to climb the helicopter and avoid surrounding hazards. He lowered collective when the helicopter was about 30 ft above ground level and held aft cyclic, but the helicopter began to spin to the left and he was unable to control the helicopter. The pilot then reduced power to IDLE using the throttle twist grip and could not recount anything further. The pilot reported no preimpact mechanical anomalies or malfunctions with the helicopter that would have precluded normal operation. He opined that he encountered a hard wind from the rear. A witness estimated that the wind was about 50 mph (43 kts) at the time of the accident.