(CNN) -- Rescuers are looking for two missing hikers after finding a third dead on the slopes of Oregon's Mount Hood, but the search has been hindered by the threat of avalanches, a sheriff's deputy said Sunday.
The hikers began their climb at about 1 a.m. PT Friday. Authorities received a call that they were missing at about 10 p.m. Friday, said Deputy Scott Meyers of the Clackamas County Sheriff's Office.
They planned a fairly easy, "semi-technical" hike in which they would come down the south side of the mountain, Meyers said.
Authorities followed what they believed to be the planned path, and on Saturday found the body of one of the hikers, identified as Luke T. Gullberg, 26, of Des Moines, Washington.
Search and rescue personnel were unable to locate the others -- Anthony Vietti, 24, of Longview, Washington, and Katie Nolan, 29, of Portland, Oregon.
"This is still called a rescue operation, at least for a couple days," Meyers said Sunday, meaning authorities hold out hope of finding the hikers alive in the freezing conditions. "We have reason to believe one of the two missing hikers has a bivvy sack, kind of like a lightweight sleeping bag. The female hiker is fairly well prepared for this climb -- she did have some stuff to warm up with."
"We're looking at the area where we found the body," he said. "We think they may have dug into that area and just can't get down."
But the threat of avalanches "is too high to go forward with a full ground rescue operation," Meyers said.
Another deputy, Jim Strovink, said there is "a high level of danger for avalanche potential on Mount Hood."
A U.S. Coast Guard C-130 aircraft was coming to help in the search, and an Oregon National Guard helicopter was flying around the area where the hikers might be, authorities said.
When the avalanche danger lowers, three teams will head to the probable areas, Meyers said.
"It could be today, it could be tomorrow," he said.
Temperatures were in the 20s overnight, with winds higher up the mountain.
The mountain rises 11,239 feet above sea level, with a vast base that stretches over 92 miles (148 kilometers). It is the highest mountain in Oregon, a dormant volcano with steam constantly spewing from holes, according to the Web site mthood.info.
CNN's Nick Valencia contributed to this report.