The blanket of orange haze currently surrounding New York City and Philadelphia may dissipate soon—at least temporarily. When air quality will improve on the east coast depends not only on how long Canadian wildfires keep burning, but also on the weather patterns that have been carrying smoke our way.
When and why did the fires start?
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The fire season in Canada runs from May to October, and it’s been starting earlier and finishing later every year, thanks to climate change. Currently, over 400 wildfires are burning, according to the Toronto Star, with more than half of those considered to be “out of control.”
Generally, about half of Canadian wildfires are started by humans—for example from a cigarette butts or improperly tended campfire. Among the rest, lightning is a common cause. We don’t know what triggered each of the 400+ fires, but we know some things about the conditions that made them possible.
This winter had very little snow, so the fire-prone areas were drier than usual as the warmer months approached. Temperatures have also been high, another contributing factor. Climate change has also weakened the jet stream, CBS News reports—that’s the weather phenomenon that moves air from west to east. The jet stream owes its existence to the difference in temperature between the Arctic and areas further south. As the cold parts of the Earth warm, that difference becomes less dramatic, and hot, dry weather systems spend more time over fire-prone areas.
How did the smoke get all the way over here?
If you’re the kind of person who zooms out on your weather app to see the storms that might be coming from far away, you’re used to watching how weather patterns move. Their exact path depends on a variety of factors that change from day to day and season to season.
When large amounts of smoke are released into the air, it can ride the wind for hundreds or even thousands of miles. Right now, winds are blowing from north to south. There’s also so much smoke in the air that it’s present even at ground level, Time reports, instead of staying at higher altitudes. That’s why we can smell it as well as see it.
What happens next?
Right now, a low pressure system sits close to Maine with high pressure to the west, the Pennsylvania EPA says in a forecast, which creates a “corridor for thick plumes of wildfire smoke to be transported southward.” The low-pressure system is expected to move eastward as the weekend approaches.
When that happens, the smoke won’t be heading straight for the east coast anymore—but it will still be produced as Canada’s wildfire season continues. Canada is fighting the fires, now with international support.