The National Weather Service expanded and extended flood watches across Washington and Oregon on Monday as a prolonged atmospheric river continues to push deep moisture into the region.
The watches now stretch from the Olympic Peninsula and Puget Sound lowlands to the Cascades, Columbia River Gorge and much of northwest Oregon, with some areas under alerts through Friday.
In Western Washington, the flood watch remains in effect for 14 counties, including King, Pierce, Snohomish, Skagit, Whatcom, Thurston, Kitsap, Mason, Island, Jefferson, Clallam, Grays Harbor, Lewis and San Juan counties.
In King County, just before 5 p.m., the Snoqualmie River reached flood phase 2, with minor flooding expected in low lying areas.
In Skagit County, major flooding is expected in Concrete and Mount Vernon on multiple days this week. The Skagit River is expected to peak on Dec. 9 at 10 a.m. and again Dec. 11 at 4 a.m. In Mount Vernon the Skagit River is expected to peak Dec. 10 at 4 a.m. and again Dec. 12.
In Cowlitz County, the Cowlitz River has spilled onto several roads in the Longview and Kelso areas, closing roads.
Forecasters warn that excessive runoff could lead to flooding in urban areas, low-lying communities, and along creeks and rivers already running high from days of steady rain.
Saturated soils will also increase the risk of landslides, especially in steep terrain and burn-scar areas.
The Portland office of the National Weather Service continues its flood watch for northwest Oregon and southwest Washington through late Thursday night.
Forecast rain totals through early Thursday range from 2.5 to 5 inches in the Portland–Vancouver metro area and lower Columbia region, with 6 to 12 inches expected in the Coast Range, Cascades and foothills.
In Central Washington, flood watches remain in place for Kittitas and Yakima counties and the eastern slopes of the Cascades, where rainfall combined with snowmelt may push rivers such as the Yakima, Naches and Klickitat toward their highest levels between Wednesday and Friday.
Chelan County’s watch was extended through Thursday afternoon due to expected periods of heavy rainfall and snowmelt, which may trigger flooding in small streams and debris flows on burn scars.
Wind Advisory in Western Washington
A Wind Advisory remains in effect until 10 p.m. Monday for much of Western Washington, including Seattle, Bellevue, Everett, the Eastside, the Snohomish County lowlands, the North Sound, the Hood Canal area and the foothills of King, Pierce, Thurston and Lewis counties.
Southwest winds of 20 to 30 mph with gusts up to 50 mph may topple tree limbs and cause scattered power outages.
Increased landslide threat through Wednesday
A Special Weather Statement from the Weather Service warns that saturated soils combined with an additional 2 to 6 inches of lowland rain and 4 to 10 inches in the mountains will sharply increase the likelihood of landslides across Western Washington.
The most at-risk areas include steep coastal bluffs, road cuts, hillsides and recently burned terrain.
The risk is expected to persist even after rainfall tapers later in the week.
Rivers most at risk of flooding this week
Hydrographs from the Northwest River Forecast Center show several river basins positioned for significant rises as rainfall intensifies in the Cascades and Olympics.
While exact peaks will depend on how much rain falls Tuesday through Thursday, forecasters say these rivers are among the most closely watched:
- Skagit River: Expected to see sharp rises midweek as heavy mountain rain drains into the upper basin. The river near Concrete is historically one of Western Washington’s most flood-prone during long-duration rain events.
- Snohomish River system: Both the Snohomish and its major tributary, the Skykomish, can react quickly to prolonged Cascade rainfall. Forecast models indicate the potential for the system to approach flood thresholds if expected rainfall verifies.
- Snoqualmie River: The middle and lower Snoqualmie Valley often sees widespread flooding during multi-day atmospheric river events. Forecasters say this week’s prolonged rain could push the river toward levels typically associated with moderate flooding.
- Cowlitz River: In southwest Washington, the Cowlitz may rise significantly as foothill and coastal mountain streams feed into the lower Columbia region. Several scenarios show at least minor flooding possible later in the week.
- Smaller creeks and tributaries: Rapid rises are possible in smaller drainages across the Cascades and Olympics, where steep terrain and saturated ground can produce sudden flooding and debris flows.
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