3 articles · Updated · The New York Times · Jul 17
Summary
Tuesday brought markedly thicker wildfire smoke across parts of Canada and the United States than in the previous few days, worsening air conditions as a persistent pattern kept feeding plumes southward.
Rapidly growing fires drove that increase, burning hot enough to generate their own weather and loft denser smoke high into the atmosphere.
Forecasters say the next 2 days are especially hard to call because smoke behavior depends on several volatile factors at once — fire intensity, upper-level winds and thunderstorms.
Friday’s expected shift in the weather pattern could change the smoke stream, but the way that transition unfolds will determine whether conditions improve or stay erratic through the weekend.