SEATTLE – Record rainfall in the Pacific Northwest triggered mudslides on Sunday as it swelled rivers and placed small towns in Washington and areas of Portland under flood threat.
Forecasters said storms were expected to dump up to 6 inches of rain in a day, and flooding was expected to be widespread.
"We're looking at the wettest storm system we've had for in almost two years," said National Weather Service meteorologist Kirby Cook in Seattle.
Portland officials warned residents in flood-prone areas such as the Johnson Creek watershed to be prepared to evacuate. The tributary empties in the Willamette River about six miles south of downtown Portland.
A mudslide near Skykomish in central Washington prompted the closure of US Highway 2 early Sunday, but crews hoped to have one lane open by midmorning. A day earlier, transportation officials said mudslides forced the suspension of Amtrak service between Portland and Seattle until Monday.
Slides blocked at least one street in Seattle and closed State Route 11, the scenic Chuckanut Drive, south of Bellingham.
The National Weather Service expects the Chehalis, Snohomish, Tolt and Snoqualmie rivers in Washington state to reach flood stage.
In southwest Washington, the Chehalis River near Grand Mound was expected to reach major flood levels Sunday afternoon and was forecast to crest at about 18 feet on Monday morning, Cook said.
The Snohomish River was expected to follow a similar path, cresting at major flood stage around 19 feet on Monday near Snohomish and Monroe. The Snoqualmie River was expected to crest Sunday in Carnation.
Officials were also closely watching the Skagit River in Skagit County.
Seattle-Tacoma International Airport set a rainfall record for the date of 1.42 inches, breaking the old mark for Dec. 11 of 1.32 inches set in 1955. Quillayute on the Pacific Coast also had a record for the date, 2.17 inches. The old record was 1.64 inches, set in 2002.
The weather service said the rain was not expected to threaten the heavily developed Green River Valley south of Seattle. Flooding has been a worry since heavy rain in January 2009 damaged a reservoir wall at Howard Hanson Dam upstream.
Cook described the storm system as a "plume of very moist, warm Pacific air." Its relative warmth brought rain, not snow into the Cascades, causing large runoff from the mountains, feeding and overwhelming rivers and creeks on the lowlands. The snow level, Cook said, was up to 10,000 feet by Saturday afternoon.
National Weather Service meteorologist Dave Elson in Portland said coastal Oregon rivers and tributaries of the Willamette River could rise out of their banks, but said the flood threat wasn't as severe as in Washington.