Seattle's heat wave and the hazy, smoky air from British Columbia are due to this phenomenon: Our usual Pacific Ocean breeze isn't blowing.

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[Seattle’s heat wave and wildfire haze could linger into next week, weather service says]

It’s one of those good-news, bad-news situations.

The smoke from fires raging in British Columbia have been swept down to the Puget Sound region by winds blowing from the interior of the continent toward the Pacific Ocean. On one hand, the wildfire smoke is harming our air quality, and people with asthma are likely to feel it. A burn ban for the region went in effect Wednesday as a result.

On the other hand? The layer of smoke acts like a sunshine shield, which happens to be deploying at the beginning of Washington state’s intense heat wave.

Here’s how the phenomenon works, according to the National Weather Service’s Seattle office:

The smoke’s particulate matter refracts some of the sun’s rays, radiating them back out into the atmosphere (think of light through a prism), said weather-service meteorologist Ted Buehner.

But those same particles are creating a barrier between land and sun, slightly lowering the predicted high for Wednesday, from 97 to 95 degrees.

 

“Envision this,” said Buehner, explaining the phenomenon. “You are in an enclosed bar with smoke and there are fans blowing at one end of the room. What’s happens? There’s no smoke at one end of the bar (with the fan), right? Now imagine that you turn off the fans and then turn on one fan at the other end of the room? What happens to the smoke?”

Well, it seeps back throughout the whole bar, he said.

We, in the Seattle area, are at the end of the bar that originally had the fans blowing on our side, keeping the smoke away.

And what are the “fans” in Buehner’s analogy? The usual cooling breeze we get from the Pacific.

The warm air we are feeling — which is also bringing smoke from the nearly two dozen B.C. fires — is blowing from the interior of the North American land mass, which is warmer, he said.

Even with the haze, which will vary in its intensity over the next couple days, Thursday is pegged to reach a high of 99 degrees at Seattle-Tacoma International Airport, Buehner said.

For air quality’s sake, the Puget Sound Clean Air Agency is  prohibiting all outdoor burning for King, Kitsap, Pierce and Snohomish counties. That means no charcoal barbecues,  fire pits,  chimineas or fire bowls,  campfires or bonfires,  wood-burning fireplaces or stoves and agricultural fires. The ban is in effect until further notice.

By Friday and Saturday, the low-level offshore flow will begin to reverse and we will see temperatures drop — as “nature’s air conditioning returns,” he said.

“Over the weekend we will be back into the 80s and 70s and it will really feel cool then,” he said.

Meanwhile, low visibility because of the smoke was causing delays averaging 47 minutes Wednesday morning at Sea-Tac Airport.

Staff reporter Scott Greenstone contributed to this story.