As of 3 p.m. on Monday, Missoula is in a Stage One Air Pollution Alert, according to the Missoula City County Health Department. 

Air Quality Specialist Ben Schmidt said a high pressure ridge has been sitting over the Missoula valley for several days, leading to the stagnant air quality.

"It started just before Thanksgiving, and has just been building slowly but surely, and now we're at a point where an air quality alert had to be called," Schmidt said. "Our basic recommendations are that people with heart of lung disease, children and the elderly should try to limit prolonged exposure and exertion as much as possible."

Schmidt said the stagnant air could remain for several days.

"Right now, there are a few weak systems getting ready to move through, but none will be strong enough to  move that cold air that's sitting in the Missoula valley out," he said. "We'll probably have poor air quality all the way through this weekend. In terms of numbers, what we look at is when the eight hour average goes over that mid 20's to 28 micrograms per cubic meter range, that's when we call a Stage One Air Alert."