Park officials said 50 searchers are looking for 32-year-old Neal Peckens of Virginia and 32-year-old Jason Hiser of Maryland. Hometowns weren't available.
Weather is the biggest challenge facing searchers, who are finding 18 inches of snow on the trail at higher elevations and five-foot drifts in some areas, spokeswoman Denise Germann said.
"The area they are working in is very steep and exposed," she said. "It's right along the Continental Divide, and it's very windy."
More rain and possibly snow in higher areas is expected on Sunday, she said. A helicopter dropped off some searchers inside the park early Sunday but Germann said low clouds moved in, preventing aerial searches.
The two were reported missing Friday after failing to catch a flight home from Montana. Their vehicle was found late Friday, and the search started Saturday.
Germann said it's not clear if they were prepared for cold weather, or if they have much experience in the backcountry. Searchers believe the two were hiking and not mountain climbing.
"We believe they are still in the park," she said. "We don't know what clothing or gear they've got."
Officials believe the two started hiking from the North Shore Trailhead at Two Medicine on the east side of the park on Tuesday and planned to return to Two Medicine on Wednesday, and then do some day hikes Thursday.
She said park rangers along with Flathead County Search and Rescue members were taking part in the search. She said some are on foot, some on horses and some searching with dogs.
The National Weather Service predicts mostly cloudy skies with a 50 percent chance of rain on Sunday with highs in the upper 50s to low 60s, dropping to the upper 30s or low 40s overnight. Winds are from the southwest at 20 to 30 mph with gusts up to 45 mph.
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