PORTLAND, Ore. — The National Weather Service has issued a Flood Watch for all of northwestern Oregon and southwestern Washington, warning of possible flooding from an incoming atmospheric river bringing heavy rain later this week.

FLOOD TIPS

The watch, issued Monday, takes effect late Wednesday night and continues through late Friday night. It covers a broad area including the Oregon Coast from Astoria to Florence, the Willamette Valley, Portland metro area, Cascade foothills, and southwestern Washington counties such as Clark and Cowlitz.

Forecasters said excessive rainfall could cause flooding of rivers, creeks, streams and low-lying areas, especially in urban zones with poor drainage. Area streams are already running high after earlier heavy rains this month, and saturated soils increase the risk.

“Landslides and debris flows are possible during this flood event,” the weather service said, noting risks to people and roads near steep slopes or canyons.

Initial heavy rain expected Thursday poses the greatest threat for urban and small-stream flooding, with river flooding likely increasing Thursday night into Friday. Numerous rivers are forecast to reach at least minor flood stage.

Residents in flood-prone areas should monitor updates and prepare for possible flood warnings.