Heat dome pushes wildfire smoke across Midwest and Northeast U.S.

New York State expanded an Air Quality Health Advisory for fine particulate matter on Wednesday, July 15, 2026, as smoke from Canadian wildfires pushed into the Northeast and Midwest. The advisory covered Long Island, New York City Metro, the Lower and Upper Hudson Valley, the Adirondacks, Eastern Lake Ontario, Central New York and Western New York, with conditions forecast to be unhealthy for sensitive groups in some regions and unhealthy in others from 10 a.m. until 11:59 p.m.

The pollutant of concern was PM2.5, fine particulate matter 2.5 microns or less in diameter that can penetrate deep into the lungs and bloodstream. It can trigger irritation, coughing, shortness of breath and other short-term health effects.

The plume was tied to large fire activity in Canada and northern Minnesota, and it could keep degrading air quality through Friday. CNN Weather projected more than 100 million people could be exposed to dangerous air across the Midwest and Northeast, including the Great Lakes, Mid-Atlantic, New York, New Jersey, Delaware and New England. Thickest smoke was expected to reach or linger over New York, Boston, Philadelphia, Baltimore, Washington, Chicago and Detroit.

The air trouble arrived as a heat dome baked much of the East and Midwest. Temperatures were already running in the 90s and triple digits, and daily records were at risk in New York City, Philadelphia, Baltimore and Atlantic City.

Toronto’s air quality ranked among the worst of any major city globally on Wednesday. Canadian wildfire management agencies tallied nearly 3,500 fires that had burned more than 4.8 million acres in Canada this summer, feeding a plume that drifted south into New York and beyond. The pattern echoed the major Canadian smoke episode of 2023, when hazardous air reached deep into the eastern and central United States.

Health officials urged people to limit outdoor activity, especially children, older adults and anyone with heart or lung disease, while air-quality alerts remained in place.