Where wildfire smoke is hitting the U.S. the hardest — and when it will end (2024)

“If you’re a New Yorker with heart or breathing issues, be careful when you’re outdoors,” said the City of New York in a tweet signed by the mayor. “Smoke from wildfires in Canada is impacting our city’s air, so an Air Quality Health Advisory has been issued. Try to limit outdoor activities today to the absolute necessities.”

In some places, air quality measurements are the worst on record. Marshall Burke, a professor of environment at Stanford University, tweeted that this event is the “[n]ear worst or worst event” in the past two decades or so, based on smoke particle data.

The source of much of the smoke pouring into the region is Quebec, Canada. Most broke out in the past week. Across Canada, there are 416 active fires, 240 of which the Canadian Interagency Forest Fire Center lists as “out of control.”

Low pressure swirling counter-clockwise over Nova Scotia, meanwhile, is making for a conveyor belt of northerly winds that is pumping the smoke south over the Great Lakes, Northeast and Mid-Atlantic.

Satellite imagery Wednesday morning showed smoke covering the Northeast and extending into the Carolinas. The thickest extended from lakes Erie and Ontario to southern New York state.

That said, hazardous air quality reached as far west as Minnesota on Tuesday, according to AirNow.gov, and into the Carolinas Wednesday morning.

Environmental agencies plastered air quality alerts across an expansive swath of the Northeast and Mid-Atlantic, in effect into Wednesday, cautioning that “sensitive individuals, including those with heart or lung disease, the elderly, and the young should limit strenuous activities and the amount of time active outdoors.”

The alerts cover southeast Michigan, parts of Ohio, northern South Carolina, much of North Carolina, northern Virginia, much of Maryland, Delaware, eastern Pennsylvania, New York, Vermont, Massachusetts, Connecticut, Rhode Island and western New Hampshire.

During Tuesday, some of the worst air quality was concentrated in western New York into Quebec and Ontario, where code red and purple conditions were prevalent, meaning air quality was hazardous for all populations.

Jase Bernhardt, a professor of meteorology at Hofstra University, determined that the Air Quality Index in Syracuse, N.Y., was the worst since reliable records began in 1999.

Particle pollution in Detroit and New York registered at the highest and second-highest levels, respectively, since 2006, Stanford’s Burke found.

Meanwhile, forecasters at the Weather Service in Burlington, Vt., called the smoke situation “uncharted territory,” having never dealt with it before. “[W]e are learning and adapting as the event unfolds,” they wrote in a discussion.

With no end in sight to the fires, the question of how long the smoke lingers comes down to wind direction.

Wednesday into Thursday, an even worse round of wildfire smoke could waft south out of Canada on the backside of a north-to-south-moving cold front. Pennsylvania, New York state and the Mid-Atlantic — including major metro areas such as Philadelphia, Newark, New York, Baltimore, Washington and Richmond — are likely to see very poor air quality. Outdoor recreation would probably be hazardous.

Winds will become more northwesterly Friday into Saturday. While that won’t fully clear the smoke, it will bring a reduction in the concentrations of fine particulate matter. Visibilities, sky conditions and air quality will improve somewhat.

Very unusual. Wildfires are normal to an extent across Canada and the western United States in the summertime, but outbreaks as widespread and numerous as these are virtually unheard of in late May into June. The amount of smoke pouring into the Northeast is thus also exceptional.

The Canadian Broadcast Corp. published a sobering graph comparing area burned thus far this year with prior years:

While wildfires can be sparked in many different ways, the rapidity with which they spread is proportional to how hot and dry the ambient environment is. There exists a strong link between the frequency and intensity of heat domes and human-caused climate change. A number of high-end heat domes have already fostered wildfire outbreaks across Canada this year, and more appear to be in the offing.

Jason Samenow contributed to this report.