A potent winter storm that descended on Yellowstone and Grand Teton national parks this weekend stranded more than 150 travelers and led a snowboarder astray into the backcountry of Grand Teton.

At its height, the storm forced the closure of the main route from Grand Teton into Yellowstone -- U.S. 26/89/91 -- a move that stranded roughly 160 travelers between Moran Junction in Grand Teton and Flagg Ranch in the John D. Rockefeller Jr. Memorial Parkway near the south entrance of Yellowstone.

"Due to whiteout conditions caused by high winds and blowing and drifting snow, Grand Teton snowplow operators were unable to keep open a 22-mile stretch of highway between the Jackson Hole Airport and Moran Junction, 30 miles north of Jackson," Grand Teton spokeswoman Jackie Skaggs said Sunday afternoon. "Out of concern for traveler safety, park rangers closed the main highway at 1:45 p.m. Marooned travelers were provided emergency shelter, food, and makeshift accommodations at Signal Mountain Lodge, Flagg Ranch, and the Moran Elementary School."

As the storm worsened Saturday afternoon, authorities determined "it was unsafe for motorists to travel beyond Moran Junction to Jackson, and so arrangements were made for overnight accommodations between Moran Junction and Flagg Ranch Resort, located 55 miles north of Jackson," said Ms. Skaggs.

"Flagg Ranch provides partial winter services, but it does not currently offer winter lodging; nevertheless, about 120 people were given shelter to see them through the night," she said in a release. "Although not open to the public during winter, Signal Mountain Lodge harbored about 25 of the stranded travelers. In addition, a dozen people used the Moran School as a temporary safe haven until the road reopened early Sunday morning."

To help keep the stranded travelers warm and somewhat comfortable, Teton Interagency fire staff gathered emergency gear, cots, and sleeping bags from the Colter Bay fire cache and Moran Fire Station for their use.

"Park rangers staffed highway barricades throughout the stormy night and rerouted motorists to the provisional shelters," said Ms. Skaggs. "Rangers at the Jackson Hole Airport Junction barricade advised travelers to return to Jackson, eight miles south, for overnight lodging. As conditions improved slightly, the highway closure shifted about 7:30 p.m. from the airport junction to Moose Junction, 12 miles north of Jackson, making it possible for some residents of the Moose area to return to their homes."

Early Sunday morning saw the park's snowplow drivers back at work, and by 7 a.m. two-way travel on U.S. 26/89/91 was restored.

Also Saturday, park rangers learned that a snowboarder had become separated from his party of six skiers and snowboarders as they exited an out-of-bounds gate at the Jackson Hole Mountain Resort and headed toward Rock Springs Bowl that afternoon.

Sam Hoerr, age 31, of Dunlap, Illinois mistakenly turned right and entered Granite Canyon in the backcountry of Grand Teton National Park, according to Ms. Skaggs. The snowboarder was able to send a text message to his companions at 2:30 p.m. and "explained that he had reached a creek and was going to follow it out; however, it was clear that he had gone astray," said Ms. Skaggs.

His companions notified Jackson Hole Mountain Resort’s ski patrol. "Given the high avalanche danger and late hour of the day, a rescue effort was launched," the park spokeswoman said.

Ultimately, 13 rescuers accessed Granite Canyon from Teton Village and begin to ski into Granite Canyon from the trailhead off the Moose-Wilson Road. Rescuers made contact with Mr. Hoerr via cell phone at 7:30 p.m. and directed him to continue down canyon following the creek, Ms. Skaggs said.

"Rescuers located Mr. Hoerr at approximately 8 p.m. and provided him with a 'split board' so that he could more easily travel out of the backcountry canyon on his own," she said. "He was then escorted out of Granite Canyon by rescuers; all returned safely to the Jackson Hole Mountain Resort around 10 p.m."

Lesson learned: "Because Mr. Hoerr was unprepared to spend a night in the backcountry—and he crossed numerous avalanche-prone areas during stormy conditions that were wind loading slopes—this situation could have become life-threatening or worse," said Ms. Skaggs. "Mr. Hoerr and most of his companions did not carry avalanche equipment with them when they exited the out-of-bounds gate. Park rangers remind skiers and snowboarders to consider weather conditions and time of day before making a decision to enter backcountry areas."