DENVER -- A potent spring storm plodded eastward Friday after dumping nearly a foot and a half of snow in the Denver area and creating havoc at airports and on highways. Blizzard conditions waned in most of the eastern plains.

As many as 400 travelers spent the night at Denver International Airport after airlines canceled about 500 flights Thursday. Air operations resumed Friday, with dominant DIA carriers United, Southwest and Frontier airlines returning to regular schedules with few cancellations.

Snow fell on the eastern plains, already socked with 8 to 12 inches, with the town of Yuma reporting 6 additional inches Friday. Winds pushed snow into drifts of more than 5 feet deep. By late Friday, the National Weather Service had dropped blizzard warnings for all but a portion of far southeastern Colorado, where total snowfall could reach 2 feet with wind gusts of 55 mph.

Three of four roads into the southeast Colorado town of Springfield were closed when blowing snow reduced visibility to near-zero.

"It was awful. Just blowing real bad," said Kelly Mason, a worker at Love's Travel Stop in Springfield, population 1,400. "Not a lot's moving around here."

Sections of three southeast Colorado highways totaling nearly 150 miles were shut down Friday.

Eastern Colorado ranchers checked on their herds, which were in the midst of calving when the storm hit.

A series of heavy storms in December 2006 and January 2007 killed an estimated 10,000 to 15,000 head of cattle in southeastern Colorado. Cattle that survived gave birth to stillborn calves because of the stressful winter, compounding losses.

"It'll have some impact, but it wasn't what we call a cow-killer," said Mike Eisenbart, who has 140 head of cattle on his ranch in Kit Carson County about 140 miles east of Denver.

Eisenbart said it would be 24 hours before ranchers know how their cattle and calves fared.

"If you feed them good, get their bellies full, get them out of the wind, cattle are pretty tough," he said.

Scores of Denver-area school districts canceled classes for a second day Friday because of icy roads and unplowed streets. Others were closed for spring break. Many government offices and courts remained closed. Highway crews briefly shut down sections of Interstate 25 in Denver on Friday to knock down icicles from overpasses.

The storm left about 20 inches of snow in the Rocky Mountains northwest of Denver and about 18 inches in the unincorporated community of Gothic, near Crested Butte, or about 120 miles southwest of Denver. Several Colorado ski resorts touted their bonanza of fresh snow.

The storm also brought Colorado's snowpack to 98 percent of the 30-year average. The snowpack is a closely watched indicator of how much water will be available for cities, farms and ranches when spring runoff begins.

More than a dozen people were treated and released after scores of vehicles crashed or slid off a 20-mile stretch of Interstate 25 in northern Colorado Thursday. The highway was reopened Friday.

Colorado State Trooper Gilbert Mares said the patrol investigated at least four chain-reaction collisions Thursday.

The American Red Cross said 285 people spent Thursday night in shelters south of Pueblo because a 40-mile stretch of I-25 was closed in southern Colorado. It has since reopened.

Gov. Bill Ritter declared a state of emergency Thursday and activated the National Guard. Troops rescued three stranded motorists and cleared a path through stalled vehicles for an emergency blood delivery, Capt. Elena O'Bryan said.