Catastrophic flooding was underway in the Pacific Northwest early the morning of Dec. 11 after an atmospheric river pounded parts of Washington and Oregon with heavy rain, covering roadways and prompting evacuations.

Forecasters warned potentially record-breaking flooding was possible along the Skagit and Snohomish rivers through Dec. 11, with overtopping of levees likely, with more flooding across the Cascade Foothills and into Puget Sound through Dec. 12.

Parts of Interstate 90 and several other roads in Washington were blocked by landslides and floodwaters with no estimated reopening time, the Washington State Department of Transportation said. Video and photos shared by the department on social media showed roads covered by flowing waters. In Pierce County, to the southeast of Seattle, the sheriff's office said its swift-water team was conducting water rescues using boats at an RV park on Dec. 10.

"This flooding is the worst I have seen here in Pierce County. Our swiftwater team has already rescued many people," Pierce County Sheriff Keith Swank said. "If told to evacuate, please do so. Don't risk your life or our deputies lives. Get somewhere safe. We will sort this all out later."

"This situation is extremely serious. The next few days are going to be very critical," Washington Gov. Bob Ferguson said after signing an emergency declaration due to the flooding. "We anticipate potentially 100,000 Washingtonians facing evacuation orders."

The atmospheric river, sometimes called a "river in the sky," was finally subsiding on Dec. 11, but the National Weather Service said lingering rain will continue to exacerbate river flooding and trigger landslides for several more days across western Washington and northwest Oregon.

"Western Washington has seen roughly 2 to 12 inches of rain in the past 72 hours, with an additional 1 to 3 inches of rain forecast throughout the day today," the weather service office serving Seattle and Tacoma said in an early Dec. 11 forecast.

Residents told to evacuate as rivers rise to dangerous levels

Skagit County, north of Seattle, was operating under a "LEVEL THREE - GO" status as of Dec. 10, with all residents who live anywhere in the 100-year floodplain (where there is a 1% risk of flooding in any given year) urged to evacuate to higher ground.

The Skagit River is expected to break records when it crests over the next couple days, the county said. The city of Concrete is expected to see the river crest at 46.13 feet and Mount Vernon will see a crest at 42.13 feet, Skagit County said.

Rivers across the region were expected to reach major flood levels at 16 points, the weather service in Seattle said the night of Dec. 10.

The Skykomish River crested above 24 feet the night of Dec. 10, just shy of breaking a record, the Snohomish County Department of Emergency Management said. At midnight, the North Fork Stillaguamish River continued rising in a major flood stage, the department said. Residents in the Tualco Valley and Sultan were also urged to evacuate.

"Low-lying homes in your area will see flooding overnight. Roads will be covered," an alert said.

Helicopter rescues save trapped residents

Multiple residents in Sultan, which houses about 5,000 people, were rescued with a Snohawk10 helicopter after becoming trapped by rising floodwaters in their homes on Mann Road on Dec. 10, the Snohomish County Sheriff's Office said.

Photos shared by the sheriff's office showed a helicopter flying and landing in a field with people carrying their belongings exiting.

The Sultan Police Department shared photos of cars submerged in floodwaters on Mount Index Road. Multiple roads were covered with water in the city.

"Please do not attempt to drive through flooded roadways," the police department said. "Please be careful, the flooding will only get worse the next couple days."

See video of a rescue of drivers caught in floodwaters

In King County, Eastside Fire and Rescue said multiple agencies worked together the night of Dec. 10 to rescue two drivers who became trapped when a river overtook a road.

They used a helicopter to rescue the drivers, one of which was on the roof of their car and the other up in a tree.

See the video:

Floodwaters may be dangerous to your health

Officials in King County warned residents to avoid certain waterways after sewage and stormwater systems overflowed during the heavy rains, potentially contaminating areas around Lake Washington, Salmon Bay, Portage Bay and Elliott Bay.

While these overflows are common during intense storms, officials advise residents to stay out of the water for at least 48 hours near the impacted sites. Exposure to the polluted water can lead to illness.

-Brandi D. Addison, USA TODAY Network

How much rain has fallen in western Washington?

The National Weather Service issued updated rainfall totals for the 72 hours ending the morning of Dec. 11. Rain totals got up to 16 inches in some places of western Washington, the weather service said.

  • Glacier: 8.4 inches
  • Finney Creek: 10.24 inches
  • Auburn: 12.1 inches
  • Howard Hanson Reservoir: 13.86 inches
  • Doty Hills: 8.9 inches

Seattle-Tacoma International Airport's rain gauge saw record daily maximum rainfall totals on Dec. 10, with 1.6 inches, breaking the record of 1.55 inches on the same date in 1977. Bellingham International Airport also saw a record of 2.28 inches, breaking the record of 0.93 inches in 2014.

This article originally appeared on USA TODAY: Catastrophic flooding sparks evacuations in Washington state. See forecast.

Reporting by Jeanine Santucci, USA TODAY / USA TODAY

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