Sometime late on May 28 or early on the 29th 2 guides and 4 clients were swept from their campsite high on Mt Rainier's Liberty Ridge. The 6 climbers tumbled down a 3,300-foot tall face and were buried on the lower glacier. After the climbers failed to return on the 30th, park rangers flew over the area on the 31st. They spotted camping and climbing equipment in debris at the bottom of the face. They also detected multiple avalanche transceiver signals, but because of dangerous snow, ice and rockfall they could not land.
At this time it is believed that an avalanche swept the climbers from their campsite located between 12,400 to 12,800 feet, but the investigation is ongoing. A short-lived but intense storm hit Mt Rainer on the 28th bringing new snow and winds to the upper mountain that would have increased the avalanche danger. While there was no fracture line visible during the search operation, a fracture line easily and quickly would have been covered up by blowing snow.
Park rangers will periodically fly over the area to monitor conditions in coming weeks and months, but recovery of the climbers is uncertain.
For now this accident is being attributed to an avalanche based on circumstantial evidence of terrain and weather conditions, as well as direct evidence observed in the runout zone.
National Park Service press release
Article at Outside Online