What happened
A public-use helicopter was participating in a joint search operation for a missing hiker located outside of a park. During the mission, the pilot landed at a remote landing zone situated in mountainous terrain to pick up seven search and rescue (SAR) personnel and one dog.
Upon landing, the pilot instructed the ground personnel to load quickly, stating an intention to avoid staying overnight at the location. The pilot used a hand gesture, holding up five fingers, which the ground personnel interpreted as a request to wait five minutes for the local obscuration to clear.
Before that time had elapsed, the helicopter initiated a vertical takeoff while still within the obscuration. The remaining SAR personnel lost visual contact with the aircraft at approximately 50 feet above ground level. They continued to hear the engine of the helicopter until they heard a collision sound, which was immediately followed by the sound of an avalanche. Following the impact and subsequent avalanche, the personnel remaining on the ground left the landing zone to seek cover.