Two powerful winter storms hammered the West Coast and Midwest, shutting down highways and snarling travel plans on one of the nation’s busiest travel days.

US media reported that Weather watches, warnings, and alerts were posted across much of the western half of the nation after a storm that had been a “bomb cyclone” marched westward from the California coast.

Hundreds of stranded cars were removed from Interstate 5 headed north from California into Oregon in the aftermath of the storm that dumped snow and created whiteout conditions on both sides of the California-Oregon border.

As the skies cleared Wednesday, drivers reported being stuck for 17 or more hours in blizzard conditions and some spent the night in their vehicles.

Farther south, winter storm warnings were in effect for the mountains near Los Angeles into early Friday with 6 to 12 inches of snow forecast for most mountains, except 12 to 24 inches for the San Gabriels, the National Weather Service in Los Angeles warned.

“Expect significant travel delays and road closures with dangerous winter driving conditions,” the weather service said.

Meanwhile, parts of the central U.S. remained under siege from a storm that delayed or canceled almost 1,000 flights in Denver alone. High winds and heavy snow forced a temporary shutdown of I-70 in parts of Colorado and across the border into Kansas. It reopened in Kansas, but the state Highway Patrol urged Kansans to stay off the roads.