Winds as strong as 100 kilometres per hour have delayed flights at the Calgary airport, blown over semis on Highway 2 and peeled off part of a vinyl school roof in Nanton south of Calgary on Wednesday.

The wind is also causing problems for firefighters battling a big fire northeast of Nanton. It started at Chinook Feeders earlier in the afternoon when a woodchip pile caught fire, and is still burning.

The Airport Authority said extremely high Chinook winds have delayed both coming and going flights at the Calgary airport.

According to the Calgary International Airport website, many flights are showing as arriving late and travellers are advised to check their flight before heading for the airport.

While Calgary's wind warning has been lifted, strong gusts are still affecting southern Alberta from Okotoks to the American border.

Strong winds near Nanton, south of Calgary, toppled the rear of this truck on Highway 2. (Tara Weber/CBC)Strong winds have also caused several vehicles to overturn along Highway 2 since Tuesday, police said.

An overturned semi-tractor temporarily closed a section of the highway Wednesday morning.

RCMP are discouraging commercial traffic from Calgary to Lethbridge because of the extreme winds, which are expected to taper off Wednesday evening.

School roof ripped off

The wind also peeled off part of the roof of a school in Nanton, 80 kilometres south of Calgary Wednesday morning.

The roof over the gymnasium of J. T. Foster High School came off in one huge piece, “like tearing a bed sheet off a bed,” RCMP said in a written release.

School principal Peter Weeks says the wind is very unusual.

"What's amazing about this wind to me is it still has not stopped, it's not gusting wind, it's just plain steady," he said.

"We're used to wind down here, we do get our fair share of it, but not like this. This is out of the ordinary for anybody."

No injuries were reported, but Stephen Harris, assistant superintendent for the Livingstone Range School Division, said the school's 180 students in grades 7 through 12 have been sent home for the day.

"Structural engineers from Calgary are currently on their way to the site to determine structural safety of the building and to determine when classes can resume," said Harris, adding it doesn't appear serious at this time.

Pauline Rees, who works at the Candy Store in Nanton, says the wild weather has people staying indoors.

"The town is a bit deserted right now because of the wind," she said. "The schools have been evacuated so all the kids are now at home. A few of the businesses have shut down for the day because the wind being the way it is, there's not a lot of traffic on the highways, so it's a bit of a ghost town in Nanton today."