Heavy rain is still expected to hit parts of Northwest Oregon and Southwest Washington beginning late Thursday.
An atmospheric river, a large mass of moisture in the atmosphere, is slated to bring rainfall to the region, according to Portland’s National Weather Service.
“The concern that we have is the sheer amount, the sheer volume of water that is coming across the Pacific Ocean and aimed right at the Pacific Northwest,” said Jon Bonk, a meteorologist with NWS Portland.
Bonk said the primary area of concern is along the Oregon Coast Range, which could see up to 10-to-12 inches of rain. Areas along the Southwest Washington coast like Pacific County and the Willapa Hills could see similarly heavy rain, Bonk said.
The Portland Metro Area and other inland areas could see 2-to-4 inches of rain.
NWS has a flood watch in effect for parts of the region from Thursday evening through Sunday morning.
The atmospheric river is only set to hit a 50-to-100-mile swath of the region, though it's not entirely clear where it will land yet, said Bonk.
“Any specific watershed is under threat right now, so we’re just asking folks to remain prepared for flooding and the details, unfortunately, are still not really going to shake out until it really happens,” he said.
Though, Bonk said, the region has stayed relatively dry, so flooding would most likely be “minor” or “nuisance” — “not impacting structures as far as businesses or homes,” he said. “However, if there’s a location that does get even 3-to-4 inches, then it is possible that an individual river could rise to a point that homes and businesses that are right along the banks of that river could be affected.”
With a flood watch also comes the potential for landslides and “debris flows,” said the Oregon Department of Geology and Mineral Industries (DOGAMI).
“Debris flows are rapidly moving, extremely destructive landslides,” said DOGAMI in a news release. “They can contain boulders and logs transported in a fast-moving soil and water slurry down steep hillsides and through narrow canyons.”
DOGAMI warns people to stay alert and travel with caution within flood watch areas.
“Historically when we’ve gotten heavy amounts of rain in short periods of time, there’s always going to be concerns of landslides,” said Bonk.