Some major areas of concern for the thunderstorms include the Cascades and eastern Douglas County, and northward into the Willamette Valley, Mr. Schaff said. He urged residents who were in warning zones to seek shelter. “If you hear thunder, go indoors,” Mr. Schaaf said.
In the scorched foothills of the Cascades, flash flooding was also a worry. Any rainfall has the potential to “run off hard and fast if there is nothing on the ground,” said Clinton Rockey, a meteorologist for the National Weather Service in Portland.
Also on Thursday, emergency teams continued to search for victims and survivors of the fires, which have killed more than 30 people, destroyed thousands of structures and burned across more than five million acres in three states so far.
The authorities are still struggling against misinformation in the fire zone.
The authorities in Western states, still locked in a grueling battle to contain fast-moving fires, struggled to tamp down waves of false rumors and misinformation that have created confusion and fear in communities directly threatened by the flames.
South of Portland, Ore., where the Beachie Creek fire is burning, county leaders pleaded with the public to trust them — about the dangers of fires and their efforts to track down each and every tip.
“I want the public to completely understand that our office has no intelligence or information about any group committing any crimes,” Sheriff Craig Roberts of Clackamas County, Ore., said in a news conference Wednesday evening. “No arrests have been made associated with any group.”
He said that efforts to trace tips often led to rumors started by “a friend of a friend,” sources that detectives could not validate, or passing observations that were spun into wild conspiracies online. In one instance, he said, two people helping evacuees noticed an abandoned gasoline can, and moved it to a safe place away from the fire. Someone called in their activity to the police, who investigated and found “they were trying to do just a good deed.”