As thousands of runners descend on the capital for race weekend there is a risk the premier events may be cancelled. Extreme heat and high humidity are threatening the marathon and half marathon.

There is a special weather statement in effect for the capital with warnings temperatures will exceed 30 degrees during the race Saturday and Sunday. For the runners who take longer to finish, the heat of the day will be at its peak.

This was a concern for runners at this year’s registration for Ottawa Race Weekend.

“Pretty nervous, a little nervous about the cancellation, a little nervous about the warm weather,” said Erin MacDonald, who is signed up for the half marathon.

Her mom, Therese Kehler, knows about the dangers of heat after running a marathon in Edmonton at 35 degrees.

“I saw a lot of people down and that was really jarring. My boss at the time was a great athlete a great runner and I passed him near the end, I said Allen let’s go, but he had fallen and the heat can really take it out of you,” Kehler said.

Organizers are debating cancelling events at the race for the first time since the inception of Ottawa Race Weekend in 1975.

“I’m not saying it’s unlikely. There are a number of different options as well beyond cancellations and that’s making some changes – we’re discussing that as well,” said race director, John Halvorsen.

At a press conference Friday, the 2007 Chicago Marathon was used as an example of what can happen to runners in extreme heat.

At that time thousands of runners took off in 29-30 degree weather. During the race hundreds fell ill, and one person later died in hospital.

“Some people get critically, critically sick,” said Medical Director, Jon Hoover. “Without intervention they would probably die. So some people asked me is it worth it? That’s a personal question but is it worth it to push it hard in this heat? No.”

Cancelling the race could also have an effect on tourism. Nearly half of the 50-thousand people signed up for the run are from out of town providing a big boost to business.

“In 2015 race weekend generated about 23.1 million dollars… people are staying in our hotels, they’re eating in our restaurants, shopping in our local stores,” said Mayor Jim Watson.

You can keep an eye on race weekend here.