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A heat dome can bring dangerously high temperatures. What is it?

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A heat dome can bring dangerously high temperatures. What is it?

People chat while having drinks under a mister at a restaurant in Phoenix on Wednesday. According to the National Weather Service, Phoenix will experience record temperatures soaring over 100 degrees due to a heat dome stemming from high pressure in the atmosphere.

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Much of the Western U.S. is experiencing extreme heat this week — with temperatures easily topping 100. Blame a condition known as a heat dome. But what is it?

If you want to visualize how a heat dome can trap a region in intensely hot weather, picture yourself making a grilled cheese sandwich.

“It almost acts like a lid on a pot,” the National Weather Service’s Alex Lamers tells NPR. He’s the operations branch chief at the Weather Prediction Center.

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“If you’ve made grilled cheese in a pan and you put a lid on there, it melts the cheese faster because the lid helps trap the heat and makes it a little bit warmer,” Lamers says. “It’s a similar concept here: You get a big high-pressure system in the upper parts of the atmosphere and it allows that heat to build underneath over multiple days.”

The heat dome that’s currently putting a hot lid on the Western U.S. will bring high temperatures that are 20 to 30 degrees hotter than normal for early June, the National Weather Service said. The forecast has both Phoenix and Las Vegas hitting 112 on Thursday, and the heat will stick around at night, falling only to the low 80s.

Here’s a guide to heat domes — and how you can stay safe:

How many people are affected by heat right now?

Some 20 million Americans, from California to Texas, were living under a federal excessive heat advisory as of Wednesday, with forecasters issuing alarms about the heat dome in the Western U.S.

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Another 11 million people were under heat advisories.

“We are bracing already here in Tucson,” says Joellen Russell, a climate scientist and distinguished professor at the University of Arizona, where she also heads the Department of Geosciences.

“We’re going to be 108 or 109 starting [Thursday], and that will persist for three days, which is consistent with our definition of a heat wave, although we’ve been over 100 now for more than a week.”

What is a heat dome?

They’re generally caused by large high-pressure systems in the atmosphere. And they’re massive, linked to a ridge of high pressure. If the term “ridge” makes you think of a mountain feature, you need to go bigger: the term refers to curves in the jet stream.

“It would typically be several states,” Lamers said of the scale. “A third to half of the country.”

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Russell says the jet stream behavior is “producing these stagnant high-pressure systems that are associated with extreme heat and drought,”

The jet stream normally spreads big storms — but right now, it’s too far north to bring moisture and potential relief to the Southwest.

“If it was blowing through Arizona, we’d be maybe even rainy,” Russell says. “But of course, it’s locked up there in northern Montana and instead where we’re experiencing warmer and warmer and warmer conditions.”

And when a heat dome sits over a large land area, Lamers says, a sort of feedback loop can take hold. High pressure typically means dry weather, which can help drive the heat even higher.

How much hotter does it get?

It depends on where you are, but if you’re enduring a heat dome, you’ll likely notice highs that are hotter than normal for that time of year. People in higher elevations, like among mountains, might avoid the worst effects.

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“But it’s definitely easier to achieve those really hot temperatures in an absolute sense at lower elevations, in valleys” and urban areas, Lamers says.

How long do heat domes usually last?

They can last anywhere from a few days to a few weeks, Lamers says. “It really just depends on the overall weather pattern.”

In Tucson, a long stretch of extremely high temperatures is in the forecast.

“We’re expecting it to be up to 108 or 109 over the next few days,” Russell says. “It’ll come back down to be in the hundreds and then it’ll go back up to very, very hot. So there won’t be a real break over the next, say, 10 days.”

But it’s hard to predict how long a heat dome will persist, because they’re linked to the behavior of the jet stream.

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“If the jet would swing south and break it up, that would be amazing — especially if it rained,” Russell says. But right now, she adds, the stream is likely to leave everyone from Idaho on south in very high heat.

Kids play in a splash pad at Riverview Park on Wednesday in Mesa, Ariz. Experts warn to make sure any outdoor play time includes plenty of water and shade — and breaks from the heat — during an extended heat wave.

Kids play in a splash pad at Riverview Park on Wednesday in Mesa, Ariz. Experts warn to make sure any outdoor play time includes plenty of water and shade — and breaks from the heat — during an extended heat wave.

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Does climate change cause heat domes?

The consensus from U.S. and international reports on climate change is that heat extremes are becoming more common, Lamers notes.

“You can get a heat dome or a configuration of the weather pattern that is similar to past cases,” he says. “But it’s going to be easier to achieve more extreme temperatures as a consequence of global warming.”

“We have more frequent heat waves now here in the U.S. and worldwide,” Russell says. “They are more frequent and they last longer.”

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How can people stay safe in a heat dome?

“Heat is actually the deadliest weather-related hazard in the United States,” Lamers says, putting it above attention-grabbing events like tornadoes and hurricanes.

“What makes them so deadly,” Russell says, “is that people don’t understand that it’s not the first day of the heat wave that kills you. It’s the third or the fourth. You know, somebody decides at lunchtime to put their laundry out and it can be less than 15 or 20 minutes and you can have heatstroke.”

Russell, who is also a member of the nonpartisan group Science Moms, says she takes extra precautions with her kids, like getting a big, wide hat for her son, who’s a lifeguard. And because of the heat, the Tucson resident says, “we’re up at 5 to walk the dog so they don’t burn their little feet on the pavement.”

Russell says pools in her area will stay open longer, to give children a safe option to play outside. She’s also a big fan of sail shades, which protect kids at splash pads and help save water.

“We’ll also have cooling stations,” she says, and libraries will be open longer hours.

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To stay safe during the day, people should take extreme heat seriously, staying hydrated and finding ways to break their exposure.

“And look out for other people in your life — neighbors, family, friends,” Lamers says. “Those community connections are really important to make sure people stay safe.”

Children, the elderly, and people with chronic conditions can be especially vulnerable. Lamers says anyone who isn’t getting a chance to cool off at night should pay special attention.

“We find this a lot, that actually the minimum temperatures have a pretty high correlation to fatality rates in these types of events,” Lamers says. “Basically, if Mother Nature isn’t allowing you to cool yourself down naturally at night with just the overnight temperatures, then it becomes really important that you find a way yourself to break that exposure to the heat.”

Track your heat risk in the U.S.

A new tool lets you see a map of dangerous heat across the contiguous country: The HeatRisk index comes from a collaboration by NOAA and the Centers for Disease Control and Prevention.

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The color-coded map has a seven-day forecast, aiming to help people understand the health risks they could face.

Level 4, or magenta, is the most extreme category, signifying “rare and/or long-duration extreme heat with little to no overnight relief” that can affect anyone who doesn’t get enough hydration or cooling to mitigate the high temperatures.

But even if your area is orange, or at Level 2, you should still take care. In those conditions, most people who are sensitive to heat will be affected — especially if they don’t have ways to cool off, and stay hydrated.

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Can the so-called nanobubbler save the Reflecting Pool? | CNN Politics

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Can the so-called nanobubbler save the Reflecting Pool? | CNN Politics

The $1.7 million “ozone nanobubbler” being used in an effort to make the Lincoln Memorial Reflecting Pool water crystal clear has a unique ability to shoot 500 million microscopic bubbles into every teaspoon of water. The injected oxygen is supposed to oxidize — or, unscientifically speaking, smash through — algae, bacteria and other chemicals.

The Trump administration has touted the technology as “state of the art.” At the onset of the project, the administration dispatched a small company based in Brookfield, Ohio — one of the only in the country with this type of technology — to lead the high-profile, high-stakes gambit to see whether the technology could work on the 6.5 million-gallon landmark that for decades has evaded cleanliness. Only five years old, the technology has never been formally used or researched on a pool.

As questions mount over President Donald Trump’s broader renovation project — which has been overcome by other problems, including a peeling bottom and allegations of vandalism — Greenwater Services, the company in charge of the pool’s water quality, has been thrust into the national spotlight. The company has recently taken on a crisis communications firm to help manage the unfamiliar political waters while it attempts to focus on the pool’s actual water.

Chas Antinone, president and chief operating officer, had a one-word answer for CNN when asked whether the company’s part of the project had gone according to plan: “Yes.”

“I’ve got no political affiliation in this thing whatsoever either way. And I don’t really care about that part,” Antinone said. “Our job was to come here and bring a technology that we think can keep the Reflecting Pool looking clean and reflect the way it is supposed to.”

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A review of campaign finance reports, both federal and in Ohio, showed no contributions made by Antinone.

But the company and its no-bid contract have been dragged into a political morass as algae returned for a time to the pool, Trump campaign donations by the owner have come to light, and the pool has become a symbol of America’s divide and what some see as the president’s failures.

And questions remain about whether the new technology will work long term, with no timeline set by the Department of Interior for the more extensive repairs to decades-old pipes that are necessary to keep the technology running.

Joe Trusty, who is the editor of Pool Magazine and has a background in pool service and construction, said the nanobubbler has been “a tremendous buzzword around our industry.”

“It’s not surprising to me that they were brought into the conversation, nor is it surprising to me that they implemented it,” he said. “Whether or not it is going to be able to be effective in as large a body of water and as shallow a body of water such as the Reflecting Pool remains to be seen.”

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Greenwater Services walked CNN through a detailed timeline of its work with the Trump administration. That accounting revealed that some accommodations were needed to meet the president’s demands to have the pool refurbished by the July Fourth celebrations marking America’s 250th birthday.

From the get-go, the company had to be nimble.

The permanent ozone nannobubbler unit had not yet been fully fabricated in Ohio for the job, and yet the pool was being refilled with water. So, the company brought in temporary equipment to get the system running before the permanent structure was finished.

Four stand-alone mobile machines, which could be seen with the naked eye, were put in the Reflecting Pool on June 6, two days after the pool was refilled with water. The units, which work differently from the permanent ones, made small white plumes of bubbles as nozzles shot nanobubbles into the water. The company said the four machines were operating at the same amount of power that the permanent system would have had.

At that point the water was clear; everything was working well, a spokesperson said.

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However, on June 12, a source close to the project said the company was asked by the National Park Service to remove the temporary structures. They were not given a reason. The four units were taken offline and off-site by the company. The algae bloom appeared, according to a person close to the project and video images of the pool captured that afternoon by a CNN camera.

Greenwater Services would not comment on the time gap when the temporary systems were removed. The Interior Department and White House did not respond to CNN’s questions about why the call was made to take the machines out of the water. The New York Times first reported on the removal of the temporary systems.

During that 24-hour period, the Trump administration hosted a high-profile Ultimate Fighting Championship photo op on the National Mall.

The next day, the company reinstalled the temporary machines.

As the four temporary units continued to run, the permanent unit arrived on June 16 and installation began. On June 25, the temporary units were removed, and the permanent system began operating on its own, according to the company.

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“What I think everyone learned is that when the system is allowed to run, it cleans the water and keeps it clean,” Erin Kramer, a spokesperson for the company, told CNN.

The permanent ozone nanobubbler technology, unlike the temporary units, is not in the Reflecting Pool itself. The technology is instead housed in a small pump house, in the US Park Police stables just off the Reflecting Pool.

CNN exclusively obtained photos of last week’s installation of the technology in the pump house with the National Park Service, showing the high-tech system that is typically kept behind closed doors.

The water, which the Interior Department confirmed is pulled from municipal water, comes in and is filtered again. This is when Greenwater Service’s technology steps in.

An oxygen concentrator pulls air in and then sends an electrical current that breaks up that O2 into pure oxygen molecules to form “ozone.” That ozone is then injected into the master water pipe, through a series of patented nozzles with pressure.

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That master pipe splits into numerous preexisting smaller pipes that run around the exterior of the Reflecting Pool, providing inputs for water to enter.

The Interior Department has previously noted the need to repair and potentially replace thousands of feet of pipes that have been in disrepair for several years.

The ozone nanobubbler relies on at least some of the pipes being viable.

Antinone said a number of the pipes are viable but was unsure how many are up and running. It is his understanding that the National Park Service intends to test to see which ones are working, he said.

The Interior Department has not responded to multiple questions about the status of the pipes and the plan for broader repair.

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Antinone said the piping system would be one of the first things to look at should the algae return.

The ozone nanobubbler technology is very new, but industry experts say it is promising.

Heather Raymond, the water quality director for the Ohio State University College of Food, Agricultural, and Environmental Sciences, has tested and researched Greenwater Service’s technology for years.

One of the key factors that make it so powerful, Raymond said, is the ability for the ozone in the powerful algae-busting bubbles to stay in the water, reacting with the water, potentially for days.

Previous versions of the technology injected the bubbles into water, where they would then rise to the surface, losing power and effectiveness.

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Raymond said the new technology carries a powerful “one-two punch” because it creates a microsystem for battling bacteria that is more biologically active.

“In addition to directly oxidizing the chemicals, they promote the growth of these bacteria that eat the chemicals.”

Raymond said her studies show an effectiveness rate in the 90th percentile for the ozone nanobubbler, recognizing it as both clean and green.

Raymond was not involved in the Reflecting Pool project and said her studies have not been funded by Greenwater Services.

The National Oceanic and Atmospheric Administration has done independent research on the technology. In research published in 2020, the federal agency said the technology effectively remediates harmful algal blooms.

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Greenwater Services has never used its technology on a pool, only for projects in waterways, such as the Tijuana River, Ohio’s Lake Newport and Florida’s Port Mayaca.

Raymond said, ideally, the nanobubbler technology could work best by getting ahead of any algae, when installed during cooler months, not during the summer when the conditions for algae — heat and sunlight — are prime.

“If you had all the time in the world, you should launch this fall or winter,” she said.

But the company was under a tight deadline to make the pool clear by July.

Greenwater Services attempted to portray the timeline, and the warm, muggy DC weather they were up against as a positive.

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“If we had put this in here and there’s no algae, we wouldn’t have learned anything,” Antinone said. “The whole goal here is to make the process better, so every time we do something, we should learn a little bit.”

Like Virginia-based Atlantic Industrial Coatings, the company enlisted to resurface the pool bottom with a blue material, Greenwater Services was allowed to bypass a competitive-bidding process that is typically done for government contracts. Greenwater was awarded a no-bid contract in April.

The company’s co-owner, J.J. Cafaro, is a longtime supporter and donor to Trump and lives near his Mar-a-Lago club in South Florida. Cafaro pleaded guilty in 2001 to conspiracy to bribe Rep. James Traficant Jr., an Ohio Democrat.

“The White House was not involved in the selection process for any contract and did not weigh in on the companies selected. Full stop,” an Interior Department spokesperson said in a statement. “These companies were selected because they had the expertise, workforce and materials needed to complete such a huge project in the timeline required to celebrate our nation’s 250th.”

The White House said in a statement that it “did not play any role in the selection process.”

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Greenwater Services has sought to distance Cafaro from its daily operations.

“He is an Ohio-based businessman who invested in the Ohio-based company after the owners showed him research done on local Ohio bodies of water,” a spokesperson said. “He has no involvement in the day-to-day operations.”

CNN reached out to Cafaro but did not receive an immediate response.

Earlier this month, Cafaro defended his company’s technology to a local Ohio newspaper, the Vindicator, saying that he believes the system is working and that much of the public scrutiny over the Reflecting Pool is from “people who don’t seem to like Trump.”

Cafaro told the newspaper he would “never” talk to the president about his company’s work with the Reflecting Pool.

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“You don’t do things to put friends in awkward positions,” he was quoted as saying.

Employees of Greenwater Solutions have been at the pool on a near daily basis since early June. They anticipate remaining through the July Fourth holiday, at least. The company tests the water daily, Antinone said.

The next step is to give time to see how the permanent machine operates on its own.

CNN spoke to the company on Friday, just one day after it went online without the support of the temporary units.

“I will tell you, the water today continues to look good, and we’ll continue to test it and see how that works,” Antinone said.

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If algae and the green-hued water returns, Antinone said the company has the capability to bring in more units to the pump house to amp up the system. Additionally, he suggested there are many other options for mitigation. Some spot treatments — potentially with temporary machines — could also be used, he said.

“We think right now, we treated it — it looks good,” he said Friday while adding, “but you know, it’s going to be 100 degrees next week.”

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Three firefighters killed on Colorado-Utah border as wildfires intensify

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Three firefighters killed on Colorado-Utah border as wildfires intensify

A helicopter drops water on the Cottonwood Fire in Beaver, Utah, on Saturday, June 27, 2026.

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Three firefighters have died and two others have been injured Saturday while they tackled blazes on the Colorado-Utah border, the U.S. Wildland Fire Service has announced. The agency said the crew members had been part of an interagency response to the Knowles and Gore fires.

“The U.S. Wildland Fire Service stands united with the USDA Forest Service in grief and in our unwavering support for the loved ones left behind,” the service said in a statement on Facebook. “Their bravery, dedication, and sacrifice will never be forgotten.”

In a press release, the Department of the Interior said that the five firefighters were involved in a “burnover incident”, which refers to when officials are unable to find an escape route, so have to shelter as best they can while a fire passes directly over them. The department said the two firefighters who survived were being treated for burn injuries.

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Fires in Utah, Colorado and Arizona have been intensifying, thanks to days of low humidity, high temperatures and strong winds. The conditions have pushed fire behavior to extremes not commonly seen in the region, stretching resources and forcing the governors of both Utah and Colorado to declare emergencies.

Cottonwood fire not yet contained

The biggest blaze is the Cottonwood Fire, burning in rugged terrain in southern Utah’s Beaver County, which has grown to more than 144 square miles and remains entirely uncontained. It is currently the largest wildfire burning anywhere in the United States.

It has already severely damaged the Eagle Point ski resort and destroyed summer cabins. Damage assessments were underway Saturday, though no final estimates of destroyed structures were yet available.

On Saturday, hundreds of residents in the towns of Marysvale, Junction and Circleville were placed on notice to leave as conditions worsened.

Also burning is the Snyder Fire, covering more than 28,000 acres. It began as the Snyder Mesa Fire on Saturday in east Utah’s Grand County, but later combined with the smaller Jones and Knowles Fires in Colorado.

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Alyssa Mason, a spokesperson assigned to the Cottonwood Fire, told NPR that crews this weekend had been dealing with single-digit humidity and wind gusts of around 45 miles per hour, on top of fuel moisture readings between 2 and 8 percent.

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Trump-backed Rep. Julia Letlow wins Louisiana Senate primary runoff

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Trump-backed Rep. Julia Letlow wins Louisiana Senate primary runoff

Rep. Julia Letlow won the Republican primary runoff for Senate in Louisiana, NBC News projects, defeating state Treasurer John Fleming in another victory for President Donald Trump’s slate of preferred candidates.

Trump endorsed Letlow early in the race, which went to a runoff after none of the GOP candidates won a majority of the initial primary vote on May 16. Trump waded into the state in an effort to oust GOP Sen. Bill Cassidy, who voted to convict Trump on impeachment charges following the Jan. 6, 2021, Capitol riot.

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See live runoff results here

Letlow was the top vote-getter in the first-round primary, winning 45%, followed by Fleming at 28%. Cassidy won just 25% and did not qualify for the runoff.

Letlow will be in a strong position to win in November in the solidly Republican state, which Trump carried by 22 points in 2024. Democrat Jamie Davis, a farmer, easily won the Democratic Senate nomination Saturday night.

Letlow has pledged to be a strong supporter of the president’s policies.

“I promise you this: When I get to the United States Senate, I will never back down from fighting for your America First agenda,” Letlow told the president during a telerally with Trump on Thursday night.

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Letlow framed the race as the choice between “a real conservative fighter in the Senate, or whether we are going to send another career politician who does not want to save our country.” She touted her support for eliminating the Senate filibuster to help pass the Save America Act, a Trump-backed measure to overhaul U.S. election laws.

Fleming also tried to make the case that he was the staunchest Trump ally in the race, taking aim at Letlow’s past support for diversity, equity and inclusion policies and foreign aid. Letlow told NBC News earlier this year that she reversed her position on DEI when she “saw it for what it was” and has since been “fighting against it.”

But Trump’s backing helped boost Letlow, who also had help on the airwaves from allied super PAC.

She also touted endorsements from other top Louisiana Republicans, led by Gov. Jeff Landry. House Majority Leader Steve Scalise and Rep. Clay Higgins also backed Letlow.

Letlow is expected to join the Senate after serving nearly three terms in the House, where she also served on the powerful Appropriations Committee. She first came to Congress in 2021 after winning a special election following the death of her late husband. Luke Letlow, a former congressional aide who won a House election in 2020, died of Covid before he was sworn into office.

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