A storm bringing the first heavy snows of autumn to a large swath of the Rockies and western plains crippled parts of Colorado and Wyoming Wednesday, forcing road closures and sending students home early as the region battled up to 2 feet of snow but braced for twice that.

The slow-moving system socked Denver commuters with treacherous driving conditions _ a strong punch for residents who were sporting short sleeves just a couple of weeks ago. Visibility fell below a quarter-mile in many areas, and forecasters warned the storm would linger at least another day.

Forecasters said some areas high in the Rocky Mountains could have 4 feet of snow by the time the storm moved out Thursday. The storm spread a blanket of white from northern Utah's Wasatch Front to western Nebraska's northern border with South Dakota.

It was the biggest October snowmaker in the Denver area since 1997, said Byron Louis, a National Weather Service hydrologist in Boulder, Colo.

The same system kicked up heavy winds and dust Tuesday in Nevada, Arizona and California.

Where the snow was falling, schools took action. Students were sent home early from suburban Denver to western Nebraska. At least three high school football playoff games set for Thursday in Nebraska were postponed. College closures included the University of Colorado in Boulder, Colorado State University in Fort Collins and Chadron State College's campuses in Nebraska.

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 blamed the storm caused 51 crashes there. 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 fatalities were reported. Myriad state highways in the region were closed, along with 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.

In parts of Colorado with lighter snowfalls, such as Colorado Springs, the roads were turning slick and icy Wednesday night.

"Snow is easier for us to deal with," said Ken Winkler, a Colorado Springs snow operations manager. "The ice is what's difficult. It's like trying to knead dough. When you hit one place, you need to hit it someplace else."

Forecasters warned the snow would continue into Thursday's morning commute. Whiteout conditions were predicted 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.

In San Diego County, wind toppled a tree onto a car in San Marcos but the couple inside escaped serious injury.

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 just east of Cheyenne, Wyo., after a rough drive across Nebraska.

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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.