Much of the northern U.S. is experiencing a sky darkened by a downright frightening layer of wildfire smoke that descended on Tuesday, prompting the cancellation of many outdoor events.

The source is a coast-to-coast belt of 250 wildfires across the northern border — a pattern so severe that the Canadian government is warning citizens that 2023 may prove to be the nation’s worst fire year ever.

Wildfires can be normal and healthy parts of an ecosystem, but today's fires can burn into unnatural infernos, producing unhealthy smoke that adversely impacts people's health thousands of miles away. Different regions, at different times of year, will have a variety of influences stoking flames. Yet the continually warming atmosphere, which turns vegetation into profoundly parched fuel, is often a significant contributor in extreme fires, as are overgrown and mismanaged forests, invasive plants, and other factors.

For Americans in the densely populated northeast, including New York City, it’s reasonable to ask when the smoke from this fire will finally clear up.

But New Yorkers and their neighbors aren’t going to like the answer.

When will the wildfire smoke be gone?

Technically speaking, that answer is no one knows. But if you’re in desperate need of relative certainty, then: at least not until after Thursday morning, according to a projection at the University of Wisconsin—Madison’s Space Science and Engineering Center.

As of this writing, the smoke, with its harmful particulate matter, gasses, and liquid droplets, is expected to get worse before it gets better. The Colorado State University website’s extremely helpful RAMMB-CIRA satellite imagery library currently (as of early Wednesday afternoon) shows a fresh cloud of smoke pouring south, through Western New York and Pennsylvania on its way to New York City.

Accuweather meteorologist Tom Kines told a local paper called The Staten Island Advance that smoke Will “still be an issue” Wednesday and Thursday, and “probably into Friday, too.”

Does the weather forecast say the smoke will clear soon?

Some light rain is expected on Friday, and water droplets like rain have been demonstrated to attract aerosol particles, making rain theoretically capable of “cleaning” the air. In practice, however, rain is not some reliable atmospheric janitor.

And remember: the smoke from this crop of wildfires first drifted into the US last month. It might dissipate, only to return in a matter of weeks thanks to a different fire, and a different atmospheric pattern.

In fact, even a strong wind and a few days of dissipation won’t fully clear out the materials lingering in the environment after the initial haze has gone away. As noted by University of Montana atmospheric chemist Bob Yokelson, speaking to Discover Magazine in 2020, low concentrations of smoke can hang around and combine with the pollution already in the air. So even when it’s gone, it still may not be gone.

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How can I plan around the wildfire smoke?

All that potential lingering is important to keep in mind as you make your plans for the next few weeks. New York City’s usually clean air is some of the most hazardous in the world right now. New York City’s real-time air quality monitor site shows a staggering jump in pollution over the past two days, but the departure of this ominous orange miasma may not coincide with a just-as-rapid return to healthy air quality.

While the air outside is hazardous, it’s a good idea to not just stay inside, but avoid things like candles and gas appliances that require ventilation you can’t provide. Your lungs need all the help they can get right now.