As of Monday, some of the smoke had moved off the Eastern Seaboard, but a high-pressure system circulated it back into the U.S. and across the Southern states.

As dozens of wildfires continue to burn across Canada, flames are sending far-reaching plumes of smoke into the sky and unhealthy air to distant places. Some of the more gigantic blazes have been delivering thick smoke that spread southward into the United States over recent days.

The pull of the foul air to Northern California was significant enough that the Bay Area Air District issued an air quality advisory. According to AirNow, a federal air-quality measuring app that measures air quality in real time, the air quality at 8:30 a.m. through much of the region was only moderately healthy.