No one saw a parachute Thursday, and if Kurt Ruppert, 29, of Lake City, Fla., survived the jump and was caught in a tree or lost in the forest, he likely died of hypothermia, a King County sheriff's sergeant said.
"We just don't think he survived at this point," Sgt. Cindi West said Monday.
Dozens of searchers were out four days "calling and calling," West said. "If he survived he wasn't conscious enough to yell to us."
It snowed Thursday night and temperatures have been in the 30s and 40s around Mount Si, a steep and heavily forested 4,200-foot peak about 30 miles east of Seattle.
Searchers covered 9 square miles before the ground search was suspended Sunday. Fog on Monday prevented a helicopter search.
Ruppert was taking turns with two friends who were waiting at the grassy landing zone when he jumped out of a helicopter at 6,500 feet and disappeared.
The webbed wing suit allows a skydiver to glide at up to 100 miles per hour, so Ruppert could have covered a lot of ground, West said.
Friends in Florida say Ruppert had been skydiving seven or eight years and was experienced in a wing suit.
There's a record of Ruppert's cellphone signal until he went up in the air and jumped or shut it off, West said. That information led to an extensive search of a quarter-square mile area, which found no sign of him.
Outlying areas where Ruppert might have landed are heavily wooded or mountain cliffs.
Ruppert carried a blue parachute in a black pack. He was dressed in a tan and green wing suit, which would make him hard to spot in the woods.
Friends of Ruppert's were with ground searchers over the weekend, but did not want to talk with reporters, West said.
"People that are out there are having a little memorial today on the mountain," said a friend in Florida, Skydive Palatka owner Art Shaffer.
"There's a lot of sad people here," he said Monday.