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The storm spread a blanket of white from northern Utah's Wasatch Front to western Nebraska's northern border with South Dakota. Forecasters said some areas high in the Rocky Mountains could have 4 feet of snow by the time the storm moved out later Thursday.
It was the biggest October snowmaker in the Denver area since 1997, said Byron Louis, a National Weather Service hydrologist in Boulder, Colo.
"The plows are out, but the roads are kind of icy and snowpacked," said Ryan Drake, traffic operations specialist for the Colorado Department of Transportation. "Be patient and take your time."
Where the snow was falling, schools took action Wednesday. Students were sent home early from suburban Denver to western Nebraska. College closures included the University of Colorado in Boulder, Colorado State University in Fort Collins and Chadron State College's campuses in Nebraska. At least three high school football playoff games set for Thursday in Nebraska were postponed.
Air travelers had to change plans, too. Denver International Airport spokeswoman Erica Gingerich said some flights were delayed as visibility fell to a quarter mile in heavy snow Wednesday afternoon. The airport warned of more delays, saying it would see a foot of snow by Thursday afternoon.
On the roads, conditions were worse. Multicar pileups were reported in Colorado and Wyoming, with countless fender-benders across the region. The Utah Highway Patrol reported 51 crashes as the storm moved through. Police departments across Colorado started asking drivers in accidents without injuries to just exchange information and report the accidents to police later.
However, no traffic deaths were reported. Myriad state highways in the region were closed, along with parts of Interstate 80 in Wyoming.
Wyoming officials said they'd had reports of about 70 crashes, most of them on I-80, before deciding to close the road.
"People are just not slowing down enough," Wyoming Department of Transportation spokesman Bruce Burrows said.
Whiteout conditions were predicted Thursday for the plains areas of eastern Colorado and Wyoming and western Nebraska.
Winds were a concern farther west, too.
Winds gusting through Southern California forced a commuter train line to shut down and knocked a tree onto a car, but no serious injuries have been reported.
The National Weather Service warned of the possibility of further gusts up to 50 mph through Thursday morning in Los Angeles and Ventura counties. Fire danger warnings were up in some areas.
Back in Wyoming, the storm brought some big rig truckers to a halt.
"The smart thing is to just shut it down and call it a day," said Donnel Farrow of Willingboro, N.J. Farrow was hauling mail from Pennsylvania to Salt Lake City but pulled over his rig at a truck stop Wednesday just east of Cheyenne, Wyo., after a rough drive across Nebraska.
Associated Press Writers Catherine Tsai in Denver, Mead Gruver and Matt Joyce in Cheyenne, Oskar Garcia in Las Vegas and Scott Sonner in Reno, Nev., contributed to this report.