Winter storms sowed more chaos across the U.S. on Thursday, shutting down much of Oregon’s largest city with almost a foot of snow and paralyzing travel from parts of the Pacific Coast all the way to the northern Plains.

The nearly 11 inches (28 centimeters) that fell in Portland amounted to the second snowiest day in the city’s history. It took drivers by surprise, stalling traffic during the Wednesday evening rush hour and trapping motorists on freeways for hours.

Some spent the night in their vehicles or abandoned them altogether as crews struggled to clear roads. Other commuters got off spun-out buses and walked in groups to safety. The National Weather Service, which had predicted only a slim chance of significant snow, planned to review its work.

The weather also knocked out power to almost a million homes and businesses in multiple states, closed schools and grounded or delayed thousands of flights. The system even brought snow to usually balmy Southern California.

Kim Upham endured a 13-hour ordeal as snow brought to a standstill the traffic on U.S. 26, a mountainous highway that connects Portland to the coast. Already treacherous because of its steep grade, the highway was covered in a sheet of ice, forcing some drivers to leave their cars in the middle of the road.

“It was so scary to have semi-trucks behind you and semi-trucks in front of you, and you know you’re on a slope,” she said.