Why does wildfire smoke sometimes drift over Seattle before we can smell it?

Often, the fires are burning more than 100 miles away. The intense heat of the wildfire lofts smoke thousands of feet into the atmosphere, where winds carry it hundreds of miles downwind.

That's why the first sign is often a hazy sky rather than smoky air at ground level.

But after the sun warms the ground during the afternoon, rising bubbles of warm air make the atmosphere more turbulent, allowing some of that smoke aloft to mix down to the surface. That's when the smell of smoke becomes more noticeable, and air quality can begin to deteriorate.

If that pattern repeats for several days—with more smoke continually streaming in and each afternoon bringing more atmospheric mixing—smoke concentrations near the ground can steadily increase, causing air quality to worsen even days after the smoke first appeared overhead.