Wildfire smoke is leading to poor air quality in parts of the Northwest and western Canada, and some of that smoke may spread to other parts of the United States. But there's a difference this time compared to what happened more than a week ago.

Where America's largest fire flare-up is right now

Almost three dozen large wildfires are burning in the northwestern U.S., according to InciWeb, mostly in the eastern plains of Oregon and Washington state.

They were first triggered last week by thunderstorms over a drought-plagued area sweltering in extreme heat, and those conditions have continued this week. Thousands of lightning strikes were detected over Oregon in just the past few days.

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(MORE: The Weather Company Labs: active wildfires & fire weather tracker)

Where will the smoke go?

Smoke from these fires is leading to unhealthy air quality in areas nearest the fires, including the popular tourist town of Bend, Oregon, and Kelowna, British Columbia, according to air quality sensors.

(WATCH: What air quality index forecasts mean)

And smoke from these fires and various others in Canada and the western U.S. has been wafting over parts of the central and eastern U.S. the past several days.

But the key, here, is that smoke has been largely above the ground.

Last week's record-smashing smoke event was due in part to a rash of wildfires in northeast Minnesota and Ontario, much closer to the Midwest and Northeast.

Since those fires were numerous, large and closer, that made it easy for north to northwest winds to tap that heavy, ground-level smoke and pump it into the Great Lakes and Northeast.

This time, since those Northwest fires are much farther away, most of the smoke you'll see the next several days in the central and eastern U.S. will be smoke high above the ground.

This smoke aloft could lead to hazy skies and colorful sunsets, but not the widespread unhealthy air quality we saw a week ago.

We can't rule out a few areas of the northern U.S. reporting code orange air quality for smoke, but again, for now, this doesn't look nearly the magnitude of the previous event.

It could happen again

As we warned about in May, this doesn't mean we won't see another major smoke event in the U.S. this summer.

Summers during a strengthening El Niño often feature a weather pattern in which winds flow southeastward out of Canada into the eastern two-thirds of the U.S.

Those El Niño summers are also hotter and drier than average in western Canada and the Northwest.

So, we could still see one or more larger-scale wildfire smoke episodes in the U.S. through August or September.

What you need to know to stay safe

Wildfire smoke is hazardous to breathe for several reasons.

It contains microscopic particulate matter much smaller than the width of a human hair that can lodge deep in the lungs and then enter your bloodstream.

It can lead to short-term effects, such as coughing, shortness of breath, a scratchy throat, runny nose and burning eyes.

Prolonged exposure to dense smoke can increase the risk of chronic lung issues and increase inflammation that could lead to heart attacks and strokes.

Check your air quality forecast before heading outside.

You can do that on The Weather Channel app by going to your local forecast, then tapping the "Breathing" button. Or, from your local forecast page on weather.com, click on the "Air Quality" button at the top.

The index is color-coded from green (good) to maroon (hazardous).

If your air quality forecast is....

• At least code orange: More sensitive groups such as those with respiratory or heart conditions, the elderly, children and those pregnant should avoid staying outside more than necessary.
• Code red, purple or maroon: Everyone should limit their time outdoors. Consider exercising indoors and if you need to walk your pet outside, do so as briefly as possible. Wear an N95 mask outside, if you have one.

(MORE: How air pollution affects you)

Jonathan Erdman is a senior meteorologist at weather.com and has been covering national and international weather since 1996. Extreme and bizarre weather are his favorite topics. Reach out to him on Bluesky, X (formerly Twitter) and Facebook.​