GEOFF BENNETT: Welcome to the "NewsHour."

For much of the country today, spending time outside has come with a cost.

A smoky haze darkened skies from Minneapolis to Detroit and beyond.

And searing heat blamed for 13 deaths in Texas spread to neighboring states.

John Yang reports on a day of extreme conditions.

JOHN YANG: Texans splashed in public fountains throughout Dallas, looking for relief from a record-breaking summer heat wave.

RICHARD, Dallas Resident: It just seems like it's getting hotter and hotter.

But, as long as you stay cool, hydrate, hey, it's all fun.

You can have fun out here.

Lots to do.

JOHN YANG: A scorching heat dome, a region of high pressure that parks and traps heat on the ground, has blanketed West Texas and much of the U.S. South, resulting in multiple days of triple-digit temperatures and suffocating humidity.

While pools and public facilities offer some temporary respite, the conditions pose serious health risks for vulnerable groups, such as homeless communities and workers who spend much of their days outside.

Earlier this month, Texas Governor Greg Abbott signed a law that will eliminate water break requirements for construction workers, beginning in September.

But even those with air conditioning on full blast now could be at risk of losing it.

The Electric Reliability Council of Texas said power use has reached all-time highs, putting pressure on the state's electrical grid.

As the blistering sun beats down on the South, up north, a different scenario.

For the second time this year, a thick layer of haze filtered the sunlight and covered the skylines of places like Chicago.

Smoke from hundreds of wildfires throughout Canada is drifting into the United States, plaguing major cities with poor air quality.

The haze is lingering over more than a dozen states, and many of the hardest-hit cities are in the Midwest.

According to the Environmental Protection Agency, Detroit saw some of the country's worst conditions today, with air quality in the hazardous range, while indexes in Chicago and Pittsburgh were at very unhealthy levels.

Today, President Biden encountered the dense smoke as he stepped off Air Force One in Chicago.

Officials warned residents in the affected regions to stay indoors and reduce activity as much as possible.

Breathing in the small particles in wildfire smoke can have lasting effects on the heart and lungs.

DARREN RILEY, CEO, JustAir: It's like you're just sitting at a campfire all day if you're outside.

And so I really warn folks.

I saw someone running earlier today, said, hey, slow down, put a mask on.

Don't overexert yourself.

The more breaths you're taking and the harder those breaths, you're inhaling campfire smoke into your lungs.

JOHN YANG: On the lakefront in Milwaukee, the haze put residents on edge.

ANDREW ESTRADA, Milwaukee Resident: It makes me want to go back home and stay inside until it's safe, because you honestly don't know what you're breathing in.

JOHN YANG: The smoke has even made its way across the Atlantic, reddening the skies in Pontevedra on Spain's western coast.

Researchers say the fires, the poor air quality, and the blazing heat are all associated with climate change.

For the "PBS NewsHour," I'm John Yang.

GEOFF BENNETT: Forecasters are calling for a cold front that should start cleansing the skies by tomorrow.

The heat in the South could begin easing this weekend.