Sgt. Katie Larson with the King County Sheriff's Office said a team of rescuers worked through the night in blizzard-like conditions to carry the female snowshoer off the mountain early Sunday.
Medics confirmed that she had died when they reached the base of the mountain, Larson said.
"The conditions yesterday were horrific," Larson said Sunday. "It took 25 rescuers about five to six hours" to bring her off the mountain in a sled.
The woman, whose identity was not known, had been hiking with her dog near a group of a dozen other people Saturday afternoon when an avalanche hit Red Mountain near Snoqualmie Pass.
She was buried in five feet of snow but was dug out with the help of the group of snowshoers who had also been caught in the avalanche.
Members of that group told authorities that it took them 45 minutes to find the woman. "They did their best to try to warm her up," Larson said.
It was the first avalanche fatality reported in Washington this season, according to the Northwest Weather and Avalanche Center in Seattle. Nationwide, 16 others have died avalanches this season, according to the Colorado Avalanche Information Center.
Meanwhile, the search for a 61-year-old hiker who was swept down the mountain in a separate avalanche at Granite Mountain on Saturday was suspended indefinitely due to the poor conditions.
The Northwest Weather and Avalanche Center said the avalanche danger in the area Monday is "considerable" above 4,000 feet.
The man, identified as Mitch Hungate, from Kent, Wash., was with two other friends when the avalanche carried them more than 1,200 feet down the mountain. The friends emerged suffered injuries that were described as not life-threatening.
Hungate, a married stepfather with a dental practice in Renton, was hiking with two other men on Granite Mountain, near milepost 47 on Interstate 90.
"They started out, everything's fine, they're in a gully-type area - when they're hit by the avalanche," Katie Larson of the King County Sheriff's Office said.
The avalanche struck shortly after 12:30 p.m. Saturday and carried all three men about 1,200 feet down the slope at speeds of more than 50 mph, according to a GPS device one of them was carrying.
Hungate, a triathlete who worked out several hours a day, disappeared. A search was launched, but no sign of the him could be found.
Kenny Kramer, director of Northwest Weather and Avalanche Center, said 20 to 30 inches of snow fell over the weekend. All that new snow was weakly attached to the old snow crust, making it more unstable, Kramer said.
"We had a considerable danger," the meteorologist said Sunday.
Avalanches during the spring aren't rare, he said, noting that there's a secondary peak of mishaps during this time because the Northwest still sees winter-type storms. When that snow falls in the spring, it often warms up quickly, creating unstable conditions, he said.