DENVER (AP) -- A powerful winter storm moving across Colorado Friday dumped more than a foot of snow in some areas as it prompted a blizzard warning, forced flight cancellations and school closures, and drew calls from highway officials to slow down on icy and snow-packed roadways.

Snow began falling Thursday night and by 3:30 a.m. MST Friday, six inches had fallen on downtown Denver, more in suburban areas and up to 15 inches in the foothills west of the city, National Weather Service meteorologist Bob Kleyla said.

"It's been pretty consistent. Snowfall rates have been about an inch per hour," he said.

Boulder and some areas just north of Colorado Springs were struggling with 10 inches of snow, Kleyla said.

Cities in the Front Range urban corridor from Colorado Springs in the south to Fort Collins and Greeley in the north were under a winter storm warning.

Despite the weather, there have been no road closings anywhere in the state, Jarrett Handy, a traffic specialist with the Colorado Department of Transportation, said early Friday.

"At the present time, roads are icy and snowpacked," he said. "Our crews are definitely out (and) doing their best to keep them open."

He urged motorists to drive cautiously, especially during rush hour.

The storm warnings prompted shoppers to stock up on food and liquor, while Colorado lawmakers canceled legislative work on Friday.

Stores in Denver reported brisk business Thursday night.

"The cheese wall is hammered, bread's kind of hammered, milk's kind of low," said Aaron McFadden, a manager at a King Soopers store.

Ted Vaca at Argonaut Liquor said customers were snapping up all kinds of drink.

"It was more like a Friday than a Thursday," he said.

A blizzard warning was issued for northeastern Colorado, where forecasters said up to 20 inches of snow could fall. Sustained winds of up to 30 mph could bring visibility to zero and make travel all but impossible.

Kleyla said the storm might not be as bad across Colorado's eastern plains as forecasters thought, but added "they're still going to get a good amount of snow."

Forecasters said up to 22 inches of snow could fall on Denver by Saturday morning, with up to a foot in Colorado Springs and 15 inches in Fort Collins.

The storm forced the cancellation of more than 150 arriving and departing flights at the Denver airport that had been scheduled through Friday night.

A Learjet ran off a runway at the Pueblo airport as the storm moved in, but investigators hadn't determined if the weather was a factor. None of the 10 people aboard was injured, the Federal Aviation Administration said.

Many school districts announced they would be closed on Friday, including the two largest, in Jefferson County and Denver.

The storm could break into the top 10 list of the heaviest snowstorms in Denver history. The city's 10th biggest dumped 22.1 inches in 1912, NWS meteorologist Chad Gimmestad said.

"We're looking at 36 hours of snow, maybe a little more than that" from this storm, Gimmestad said.

Denver's record is 45.7 inches from a 5-day wallop in 1913.

Parts of Wyoming, Nebraska, Iowa and Kansas were also predicted to be hit by the storm