A search is under way at Denali National Park and Preserve for two Japanese climbers who failed to descend from Mount McKinley on schedule. Poor weather has been hampering search efforts.

The two were climbing on the Cassin Ridge of Mt. McKinley, North America's tallest mountain at 20,320 feet. Clouds and high wind in the Alaska Range kept the high-altitude Lama helicopter on standby all day Friday, May 23, though weather conditions allowed a preliminary aerial search to an elevation of 12,000-feet on Saturday morning May 24. The climbers were not spotted.

The two men were expected to return from their climb of the Cassin Ridge by May 22. The team has been climbing in the Alaska Range since April 7, including several technical peaks in the Ruth Gorge.

As is common for climbers attempting the challenging Cassin Ridge route, the climbers made an acclimatizing ascent of the West Buttress in early May, reaching Denali Pass at 18,200 feet. The team was reportedly last seen by another climbing party on May 9 at their camp at 7,800 feet near the mouth of the Northeast Fork of the Kahiltna Glacier, the team’s intended approach route to the ridge.

It is uncertain what day they began their ascent of the Cassin Ridge, a technically difficult climbing route that involves a 1-to-2 day approach, plus 3 to 6 days climbing on the route itself. The Cassin Ridge features steep, 55- to 75-degree slopes of mixed snow, ice, and rock. According to their stated intentions, the men planned to descend the mountain via the West Buttress, which would take an additional 1 to 2 days.

Weather conditions during the past two weeks have been somewhat variable in the Alaska Range, but not severe. However, the National Weather Service has issued a high wind warning for Mt. McKinley through the Memorial Day weekend, with winds from the south peaking at 100 to 110 mph at elevations above 17,200-feet. Winds have been strong at the 14,200-foot camp as well, ranging from 20 to 30 mph with gusts to 60 mph.

The National Park Service will resume the aerial search as soon as weather permits.