Heavy rain could cause flooding and landslides, and high winds could add to the morass by toppling rain-soaked trees into power lines and across roads, local officials warned Monday.
A flood watch began at 10 a.m. and will extend through late Thursday night, the Portland office of the National Weather Service said.
"Excessive runoff may result in flooding of rivers, creeks, streams, and other low-lying and flood-prone locations. Landslides and debris flows are possible during this flood event. People, structures, and roads located below steep slopes, in canyons, and near the mouths of canyons may be at serious risk from rapidly moving landslides," the federal agency said.
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Anywhere from six to 12 inches of rain could fall across the region, the NWS said.
"Urban flooding is possible and water on roadways will increase the risk of hydroplaning and car accidents," the agency added.
A wind advisory in effect from 7 a.m. Monday morning through 4 a.m. Tuesday could also cause problems, with southwest winds of 15 to 25 mph and peak gusts of up to 35 to 45 mph in the forecast.
"Isolated downed trees and power lines could cause power outages. Never approach downed power lines," the NWS said.
'A debris flow moves faster than a person can run:' DOGAMI warns of slides, debris flows
Landslides and debris slides could occur as a result of the rain, the Oregon Department of Geology and Mineral Industries (DOGAMI) said.
"Debris flows are rapidly moving, extremely destructive landslides. They can contain boulders and logs transported in a fast-moving soil and water slurry down steep hillsides and through narrow canyons. They can easily travel a mile or more. A debris flow moves faster than a person can run. People, structures, and roads located below steep slopes in canyons and near the mouths of canyons may be at serious risk," the state agency said.
To stay safe, DOGAMI urged these steps:
- Stay alert. Track the flood watch by radio, TV, weather radio, or online. If told to evacuate, do so immediately.
- Listen. Unusual sounds might indicate moving debris, such as trees cracking or boulders knocking together. A trickle of falling mud or debris may precede larger landslides. If you think there is danger of a landslide, leave immediately.
- Watch the water. If water in a stream or creek suddenly turns muddy or the amount of water flowing suddenly decreases or increases, this is a warning that the flow has been affected upstream. You should immediately leave the area because a debris flow may soon be coming downstream.
- Travel with extreme caution. Assume roads are not safe. Be alert when driving, especially at night. Embankments along roadsides may fail, sending rock and debris onto the road.
