This story originally appeared in the Morning Brief email newsletter. Sign up hereto get more stories like this and weekday weather updates from The Weather Channel and our meteorologists. F​or real-time data, check our exclusive The Weather Channel air quality hub. Last week was the from a rash of Canadian wildfires. It set particulate pollution records in Chicago, Detroit and Pittsburgh, among other cities. Now computer forecast models are suggesting a U-shaped “trough” of low pressure will set up next...