Corridor
Most smoke in the eastern half of the continent is Canadian, and it is old by the time it arrives.
This corridor starts in the boreal forest of northern Manitoba, northwestern Ontario, Saskatchewan, and Quebec, and runs south and east on northerly and northwesterly flow. Nothing in the American West has to be burning for it to run. That is the single most useful thing to know about it, and the thing that surprises people most: a bad air day in Detroit or Boston often has no upwind fire anywhere in the United States.
The cities on it are not interchangeable, because they sit at different distances from the source. Winnipeg is usually the source end rather than the receiving end, and gets smoke fresh and concentrated a few hundred kilometres from the fire. Minneapolis is one of the first major American cities the same plume reaches, often in under a day, which is why Minnesota air quality alerts frequently fire before anyone else in the corridor issues one. Toronto sits close enough to northern Ontario and Quebec to get smoke thick rather than aged. Chicago, Milwaukee, Detroit, and Cleveland are a day behind that. Boston, New York, and Philadelphia are a day behind again, far enough downwind that smoke usually arrives aloft and then mixes down through the day.
That delay is the reason this corridor is worth reading as a corridor. A plume that is over Winnipeg this afternoon is a forecast problem for Minneapolis tonight and for the Great Lakes tomorrow, and the upwind link on each city page below points at whichever city usually sees it first.
Two local mechanisms then decide how bad it gets after the smoke arrives. The Great Lakes give a plume a clean run with nothing to break it up, and the lake breeze can pin it against a shoreline through the afternoon. Conditions on Milwaukee’s or Cleveland’s lakefront and conditions ten miles inland can differ noticeably on the same hour. Pittsburgh has the opposite problem: cool air settles into the river valleys overnight and caps them, so a plume that would pass over a flatter city sits instead.
June 2023 is the event the whole corridor shares. Quebec smoke put Toronto, Detroit, Cleveland, Milwaukee, Chicago, Pittsburgh, Philadelphia, Boston, and New York into their worst air in living memory inside the same week, and June 7 in New York produced the orange-sky images most Americans now picture when they hear the phrase wildfire smoke. The 2023 season overall was the worst wildfire year in Canadian history by area burned.
Listed in the order the smoke reaches them, not alphabetically. Each level here is read when this page loads and carries the time it was read. Open a city for its clear time and the rest of the forecast. Each page also carries that city's own distances and its own named sightlines, so you can check a level against what you can actually see from there.
Smokeshow is for informational and educational purposes only. It is not health, medical, or safety advice. Forecasts are model estimates and can be wrong, sometimes by a lot. Descriptions of what you might smell, see, or feel are generalizations, not predictions about your body. For decisions about your health, outdoor activity, or air quality safety, rely on official sources like AirNow.gov, the National Weather Service, and your local health authorities, and talk to a medical professional about your own situation.