DENVER (KDVR) — If you spent any time outside Friday or Saturday you probably saw a thick haze in the sky. It’s all due to smoke coming from large wildfires up in Canada.

“Now we’re on a streak of day two, tomorrow will bring more smoke and we will potentially see some of the worst air quality in the world not just the country,” Pinpoint Meteorologist Liz McGiffin said Saturday.

McGiffin explained the smoke comes in on a northeasterly breeze and then settles across the Front Range. She said the mountains to the west, not very visible on Saturday, work as a wall with the smoke not making it easy to push out.

“It almost traps it in the Front Range as it pushes against the mountain range and that’s why areas like here in Denver, we notice the thick blanket of smoke,” McGiffin said. “It’s like a fog at times where you can’t see the mountains.”

While Colorado is dealing with poor air quality, thousands of runners are expected to lace up for the Denver Colfax Marathon.

“There will likely be a group of runners who have had experience with this and know not to run in this type of air quality,” National Jewish Health pulmonologist Dr. David Beuther, who is also participating in the race tomorrow, said.

Beuther said most healthy people might experience things like a scratchy throat or cough and anticipates they will still show up for the race. But he said people sensitive to air quality might have trouble with extended exposure outside.

“During the race, your performance might not be what you expected it to be or trained for,” Beuther said.

Denver Colfax Marathon posted on its website Saturday:

“Air quality advisory indicates unhealthy for groups with underlying lung conditions. If you have picked up your race packet including bib but no longer feel comfortable running on Sunday, please feel free to run virtually and send results to info@RunColfax.org and we will mail you your medal.”

Beuther said it’s important to lower your performance expectations and listen to your body if it’s telling you to go inside and get out of poor air quality conditions.

“We’re really learning to live through this. It seems like the past five to 10 years we haven’t gone a summer without the smoke,” Beuther said.