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Boston Globe

Haze from Canadian wildfires has returned to New England. Is this the new normal?

So far, this season has triggered memories of 2023, when record-setting Canadian wildfires burned 42.7 million acres and smoke drifted downwind to New England. Fast forward to 2025. More than 200 active wildfires are raging across Central and Western Canada with more than 8.6 million acres burned — about the size of Massachusetts and Connecticut combined. More than half the blazes remain out of control. And get this: About a dozen 'zombie' fires have been smoldering and burning for the past two years. The key difference between 2023 and now is that the fires are burning much farther west in Canada so far this season, giving time for the smoke to rise higher in the atmosphere by the time haze arrives here, limiting the impacts. Advertisement How the weather pattern brings smoke to New England So how is wildfire smoke from over a thousand miles away coming to New England? The equation is rather simple. Wildfires send hot smoke high into the atmosphere, eventually reaching the steering pattern or jet stream (remember this is the highway that storms often travel along), transporting the smoke eastward. Then surface-level systems tug at the smoke and disperse it according to wind direction. Whether the smoke reaches the surface depends on wind direction, speed, and temperature profiles in the atmosphere. Advertisement In this case, the Canadian wildfire smoke is reaching the mid- and upper levels of the atmosphere because the volume of wildfires is producing excessive heat, making the smoke much hotter than the surrounding environment at the surface. Hot air rises until it reaches the same temperature as its surrounding environment. Below are a few examples of how smoke disperses. Currently, we're seeing intense wildfires across unstable and well-mixed atmospheres across Canada. Check out examples (c) and (d). Examples of wildfire smoke dispersion. The Canadian fires are examples of (c) and (d): smoke penetrating high up and traveling long distances. ResearchGate Elevated smoke vs. near-surface smoke The difference between us seeing a glowing red sunset or deteriorating air quality with alerts about harmful impacts comes down to how high the smoke is in the atmosphere. 'The atmosphere is very dynamic and how much of this smoke is 'elevated' in the upper atmosphere and how much is 'near-surface' are important distinctions,' said Donald Dumont, meteorologist at the National Oceanic and Atmospheric Administration. The most common weather setup leading to smoke reaching near the surface and smelling of a campfire is a well-mixed atmosphere. Remember when I said smoke rises high into the jet stream and travels thousands of miles? Well, during that trip the smoke is cool and becomes more dense. When you reach a well-mixed atmosphere (when it is generally warmer in the mid- and upper atmosphere than usual), the cool, denser smoke can sink to the surface. 'More locally to Boston, there will be a chance to see more instances of smoke and haze, so long as the fires burn across Canada,' said Francis Tarasiewicz, a meteorologist at NWS Norton. Advertisement Quick stat: Smoke is considered 'near the surface' when it is around 25 to 30 feet above the ground. If the atmosphere is stable before smoke arrives, there's a good chance that smoke will stay elevated. In a stable environment, air hardly moves vertically because there are layers in the atmosphere with warm or cool temperatures trapped. Those layers act as lids, not allowing smoke to sink beyond a certain height — and keeping folks on the ground away from potentially harmful pollutants. 'In general, the further away from New England the smoke plume is, the more likely it will be lifted to the upper atmosphere,' said Dumont. 'This is what leads to that opaque white sky and red sunsets. When the smoke source is closer to us, let's say Quebec or Ottawa provinces, the smoke is more likely to be near-surface and more of an impact.' Max Deluty, 12, working on his golf game at Granite Links Golf Course. Matthew J. Lee/Globe Staff Difference this year vs. 2023 The distance of the active fires from New England matters significantly. Two summers ago, in 2023, most of the wildfires in Canada were across Eastern and Central Canada, and much of the smoke was near the surface across Boston and New England. The region often was under the same pocket of high pressure as Eastern Canada, where smoke would be trapped near the surface. There were many days in the summer of 2023 when air quality was moderate to unhealthy. So far this year, the Canadian fires have been much farther west, meaning the smoke will generally be suspended high in the atmosphere and, for now, have less impact. Depending on the wind direction of our surface systems, New England will likely deal with bouts of wildfire smoke through September. Advertisement Ken Mahan can be reached at