The pair were unprepared for hiking in winter conditions: no sleeping bags, matches, phones, or any way of calling for help. They spent a brutal night on the mountain, both men succumbing to hypothermia before rescuers using a helicopter found them the next day. Osborne lost part of his right leg; Frederickson lost his life.

Osborne’s is but one of the many unforgiving lessons the White Mountains deliver on a regular basis to any hiker who underestimates its harsh and unpredictable conditions: In an eerie echo of the tragedy 16 years ago, on Thursday, another winter hiker suffered severe hypothermia and had to be rescued by helicopter from the very same mountain after becoming trapped overnight by deep snow and freezing conditions.

“People underestimate just how unforgiving the White Mountains can be,” said Ty Gagne, an avid hiker and author of three books about trouble in the White Mountains, including Osborne’s case. “I think there’s a certain amount of complacency that can happen because they’re four to six thousand feet.”

There have been more than 60 search-and-rescue efforts in the Whites just since June, including one in November in which two siblings had become hypothermic while hiking on the Lincoln Brook Trail. And, in the last five years alone, at least 20 more people have died in the White Mountains.

New Hampshire usually averages more than 100 hiker rescues a year, roughly half of them in the Whites, according to a New England-based hiking podcast group that tallied search-and -escue information from the New Hampshire Fish and Game Department.

With its easy access and proximity to large urban centers, the Whites have long been a destination for millions of hikers annually. The range boasts panoramic vistas, pristine lakes, and lush forests, plus the highest peak in the Northeast: Mount Washington, which stands at nearly 6,300 feet.

But the allure can also bring danger.

Climbers can easily get injured in the steep, uneven terrain. Since 2019, more than 250 hikers in New Hampshire have been rescued with lower leg injuries. About 40 succumbed to fatigue. Nearly 150 panicked or got lost.

“The mountains don’t care. They don’t discriminate,” said Gagne. “It doesn’t matter if you’re coming there with a young family, or if you’ve climbed 14,000 footers out west … the mountains aren’t going to relent. It can be a really unpredictable, unforgiving environment.”

As the winter weather descends on New England, the danger can compound.

“The clock is on, the second you’re immobile. Hypothermia sets in very quickly” said Mike McLaughlin, an experienced hiker and host of the Sounds Like a Search and Rescue podcast. “If you feel like you’re in a situation where you can’t get out, call for a rescue immediately.”

Franconia Ridge consistently requires the most rescues, with 68 in the past five years, data show. Mount Washington and Mount Chocorua were not far behind, with 60 and 42 rescues, respectively. All three are in the White Mountains.

Most rescue operations aren’t swift or easy, officials caution.

People “think you’re going to swoop in with a helicopter and pick them up. That’s not the way it works. It’s going to take three to four hours,” said Kevin Jordan, chief of law enforcement for New Hampshire Fish and Game.

Jordan leads a team of more than 40 search-and-rescue officers across six districts in New Hampshire. The group completed nearly 2,000 missions between 2009 and 2019, according to a report from the department.

In some cases, Jordan said, rescues had to be called off because weather conditions were too hazardous. Two of his officers are out with injuries for December.

The New Hampshire Fish and Game Department, which carries out most hiker rescues, recommends packing the following essential items for winter hiking: a map, compass, headlamp, fire starter, first aid kit, whistle, knife, warm clothing, extra food and water, and rain jackets and pants.

They also run the Hike Safe program, where hikers can buy a card that covers the cost of search-and-rescue operations in emergencies. The website also has additional safety tips.

Osborne and other rescued hikers say the work that Fish and Game does is crucial.

“They just have an incredibly important role for the protection of people,” said Osborne. Without rescuers, “plenty of people wouldn’t be here.”

Neena Hagen can be reached at neena.hagen@globe.com.