The search for Kurt Ruppert, 29, of Lake City, Fla., was suspended when darkness fell Friday evening, and efforts to locate him will resume Saturday, said King County sheriff's Sgt. Cindi West.
When Ruppert jumped Thursday afternoon, he was wearing a special wing suit with fabric under the arms to allow him to glide like a flying squirrel.
Searchers were hoping Ruppert was stuck in a tree with his parachute or perhaps lost in rugged state-owned land around 4,200-foot Mount Si, West said.
Authorities know the flight pattern of the aircraft, but a number of factors have made it difficult to find Ruppert. West said she was told wing suit flyers don't deploy parachutes until they reach an altitude of 2,000 feet.
"The speed and height of the jump would enable him to travel a large distance in a short amount of time," West said.
About four-dozen people began searching for Ruppert on Thursday, then resumed the effort at daybreak Friday in a 5-square-mile area that includes Mount Si, which is covered with trees on steep slopes. It's popular with hikers even though it can be treacherous.
"We've got a lot of search and rescues up here every year," West said. "It's dangerous and difficult. The footing is bad and there are lots of cliffs."
It was foggy Friday morning, but the weather cleared enough for a helicopter to join the search. The temperature was in the 40s, and Ruppert isn't dressed or equipped to stay out overnight, authorities said.
Ruppert was wearing a brown and green jumpsuit that likely blends into the terrain.
He was skydiving with two friends, and they were taking turns jumping from the helicopter. The friends were waiting at a grassy landing area, but no one saw whether Ruppert's chute deployed.
"The guys on the ground could not see where he jumped from their angle, and the pilot couldn't see when he went out the door because he was focused on flying," West said.
Ruppert has been skydiving seven or eight years and is good at handling a wing suit, said a friend, Art Shaffer, owner of Skydive Palatka in Palatka, Fla.
Shaffer jumped with Ruppert at midnight on New Year's Eve and said Ruppert left Tuesday to jump with friends in Washington.
Ruppert is single and once owned a landscaping business, said Shaffer, who is in contact with Ruppert's family and friends.
"We've got our fingers crossed," he said.