DENVER -- Denver International Airport received some flack Thursday morning for how it's dealing with this snowstorm. Airlines were reporting three to four hour delays because there weren't enough runways cleared.

"On some days, DIA really knocks it out of the park. Yesterday, we ran a phenomenal operation considering the snow we had, so I think it's all just situational ... It hasn't been going as well today," Frontier Airlines spokeswoman Lindsey Purves said Thursday.

DIA said the storm conditions on Thursday are much worse than Wednesday's conditions, but their snow-removal procedures and plan are working.

"Today's conditions were a little more severe than yesterday's, especially overnight. The surface temperatures of the runway got rather low. It was exacerbated by high winds as well as blowing snow and there's a little bit more of snow accumulation out there," said DIA Director of Operations John Kinney.

At a news conference at 11 a.m. Thursday, DIA said it can clear runways of snow in 17 minutes, and it's done so 51 times since the storm started. However, the problem has been the blowing snow. Snow crews are battling 50 mph wind gusts.

Other airports around the country are protected by surrounding buildings, but DIA is out in the open plains, Kinney said.

Kinney said he has 174 pieces of snow removal equipment working around the clock.

"I think the removal effort has been successful today ... We've been predictable. Actually, the weather forecast was rather predictable for this storm, which helps us out immensely," Kinney said.

As the day progresses, the situation appears to be improving, but airline passengers are still dealing with delays of several hours.

United Airlines canceled about half of its flights into and out of DIA on Thursday.

Frontier Airlines canceled 19 of its flights and of those flights that were making it out, the planes were dealing with three- and four-hour air traffic control delays because DIA was down to two runways Thursday morning.

DIA normally has six runways open -- two east-west runways and four north-south runways. During severe snow days, the two east-west runways are taken out of commission because of the danger of high winds.

An airport spokesman said DIA plans to have six runways open later today.

On Wednesday, there were relatively few delays and cancellations at DIA.

United Airlines has waived its change fees so you can rebook your Thursday flight without penalty. Other airlines implemented the same policy earlier this week.

If you are traveling out of Denver Thursday or Friday, call your airline or check its Web site to confirm that your flight has not been canceled.