DENVER -- Rangers at Denali National Park in Alaska have suspended the aerial search for a Centennial man who hasn't been seen since attempting to summit North America's highest peak alone.

Dr. Gerald Myers disappeared on May 19 after he was spotted at 19,000 feet ascending 20,320-foot-high Mt. McKinley, also known as Denali.

"In light of his limited supplies and the subzero temperatures, search managers consider that survival is outside the window of possibility," a news release from park rangers stated.

The active search effort for Myers was scaled back on Tuesday afternoon after search managers determined that further air operations were unlikely to locate him. Rangers said there had been no sighting of the Colorado chiropractor or his gear during six days of aerial and ground searching.

"Although no more aerial flights are anticipated, ranger staff will continue to search through the thousands of high resolution images taken during the aerial flights in search of clues to Dr. Myers whereabouts," the release said.

Myers began his summit bid from a 14,200-foot camp the morning of May 19. He was sighted at various elevations along the West Buttress route that day, the highest of which was somewhere between 18,000 and 19,000 feet, according to park rangers. Myers did not return to the high camp on Tuesday night and his fellow climbers who had remained at the camp reported him overdue.

"An individual climber was observed on the summit ridge the afternoon of Wednesday, May 20, although it cannot be confirmed that it was Dr. Myers," rangers said.

Myers was carrying only a small daypack with minimal survival gear at the time of his disappearance. He did not take a stove for melting snow, and it is unknown how much food he had in his pack.