Officials are warning drivers of a possible road condition that could cause delays and gridlock.
State Highway Patrol troopers are warning that motorists will have to use alternate routes and make extra stops.
The road conditions are described as “near impossible,” and they can’t be fully predicted.
State officials said they’re working with the Oregon Department of Transportation to determine the cause.
Traffic on Oregon’s east-west highways is expected to be backed up by the Oregon National Guard.
Motorists on Interstate 5 and the state’s two main arterials are also experiencing delays, and the Oregon Turnpike Authority has increased traffic control in both directions to keep drivers on the road.
Drivers are being urged to use extra caution on state roads, especially in Oregon’s rural areas.
The road conditions come a day after a tractor-trailer overturned on Interstate 84 near Bend.
The driver was able to get out safely, but a tow truck overturned and was killed.