Stormy conditions early in the day snarled traffic on Interstate 5 around Salem and Albany.
As many of 25 vehicles collided in clusters in southbound lanes near Albany, the state Department of Transportation said. A detour was then blocked by another crash.
No injuries were immediately reported.
“It’s pure chaos,” Oregon State Police Lt. Steve Mitchell said as troopers struggled to reach trucks and cars that crashed along the freeway. “For all intents and purposes, it’s shut down between Albany and Salem.”
Transportation spokesman Rick Little said it might be mid-afternoon before the wreckage was cleared.
“Everyone is just sitting and waiting,” he said.
Portland braced for a wicked afternoon commute, with three to seven inches of snow expected in that area.
The transportation agency said motorists should stay off highways if possible to avoid the kind of traffic nightmare that occurred in Atlanta last month when thousands of motorists were stranded.
National Weather Service forecasters said the storm will be the most widespread snow event in the northern and central Willamette Valley since December 2009. Little said it appeared three to five inches fell rapidly before the Albany crashes.
The storm is developing as moisture from the coast collides with an arctic air mass over the state. The cold is expected to last through the weekend, and a mix of snow and freezing rain could accompany moderating temperatures.
The drought has meant a slow start for many ski areas and sparked worries about the snowpack that supplies irrigation, hydropower and municipal water supplies in the state. A federal report on moisture conditions is due Friday.
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