The first avalanche, on Granite Mountain, injured two snowshoers and left one man missing. The site is off 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," said Sgt. Katie Larson of the King County Sheriff's Office.
"One of the climbers tells me that they had no warning. The avalanche, at this point, from what he's describing, is 30 feet wide, eight feet deep and about a quarter-mile long," she added.
Larson said one of the hikers was carrying a GPS device, which showed that they were carried more than 1,200 feet down the mountain in the avalanche at speeds of up to 53 mph.
One survivor has a shoulder injury, the other an injured hamstring. Both men are from the Kent-Auburn area.
They were apparently among other snowshoers up in that area who are now helping with the search for the still-missing hiker, a 60-year-old man who is also from the Auburn area.
The second avalanche, on Red Mountain near milepost 52 in the vicinity of the Alpental Ski Area off I-90, struck as a group of 13 people were snowshoeing in the area.
Two people were initially were reported missing, but one was later found alive beneath the snow against a tree. His friends dug him out and he later said he thought it was the end.
"I thought I was dying,'" said the hiker, Chris Soun. "... I couldn't see anything."
Crews continued looking for the second person, a woman with a dog who was following the group. She eventually was found alive, buried under six feet of snow.
They began digging and were able to free her from the heavy snow. Her condition was not immediately known, and officials said she could have internal injuries or hypothermia.
Witnesses said it was an incredibly close call for the group of snowshoers who set off from near the Alpental Ski Area
Soun said the group was about 2 1/2 miles into the wilderness when the avalanche roared down, splitting the group.
The avalanches came down the mountains as heavy snow fell in the Cascade Mountains from a weather system moving in from the Gulf of Alaska.
Rescuers were hampered all day by treacherous conditions. There was no word on whether the search for the missing snowshoer would continue after dark.