Science
Heat wave or heat dome? Yes, there's a difference
It sounds like something out of a horror movie, like “The Blob” or “Godzilla.” But “heat domes” are far from fiction — and the West could be facing one this week.
The term “heat dome” refers to a ridge of high pressure that persists over a large geographical region, delivering high temperatures that linger for days or weeks on end.
An infamous heat dome occurred in 2021, when triple-digit temperatures stifled the Pacific Northwest for 27 days, contributing to hundreds of deaths and spawning multiple research studies.
Experts say it’s not the same as a heat wave, which is conventionally defined as a spell of three or more abnormally hot days. But the term has gained prominence in recent years as climate change, El Niño and other variables have warmed global temperatures, shifted weather patterns and contributed to worsening hazards.
The term “does seem to have caught on in the past decade or less,” said John Abatzoglou, a professor of climatology at UC Merced, who co-authored a recent study about the 2021 heat dome.
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He said one authority on the issue is the American Meteorological Society, which maintains a glossary of such terms. That group added “heat dome” to its index in March 2022, defining it as “an exceptionally hot air mass that develops when high pressure aloft prevents warm air below from rising, thus trapping the warm air as if it were in a dome.”
Abatzoglou expanded on the definition even further, noting that heat domes aren’t just large and persistent, but typically set up over land and in warm seasons.
“We can have heat waves without heat domes,” he said, particularly in coastal Southern California, where offshore winds can bring hot temperatures south and west of the mountains while other parts of California stay cooler.
“Generally heat domes instead affect very large geographic areas — synchronizing hot and sometimes very dry conditions — which can lead to additional challenges that may not materialize with ‘local’ heat wave events,” he said.
Not everyone agrees, however. The National Weather Service has no official definition for “heat dome” in its glossary, and meteorologists there are less likely to use the term.
“I’ve heard in the media the term ‘heat dome,’ but we really don’t use that,” said Dan Harty, a meteorologist with the National Weather Service in Hanford. “Heat wave is typically what we refer to.”
Harty said the NWS typically defines a heat wave as at least two consecutive days of high heat risk. He said the incoming event is expected to peak in the Central Valley on Thursday with temperatures as hot as 108 degrees in Fresno and 107 degrees in Madera, both of which could set daily records.
The agency has issued an excessive heat warning that stretches from portions of Los Angeles almost to the Oregon border through Friday, advising residents of dangerously hot conditions and increased potential for heat-related illnesses.
Sara Purdue, a meteorologist with the NWS in Sacramento, said either term could be used for the incoming event, but “it’s not a particularly impressive heat dome.” The heat is expected to dissipate in the region slightly by the weekend, but could be followed by more heat next week.
“Usually when people refer to a heat dome, it’s stationary for whatever reason, so it’s not moving quickly out of the area,” she said. “It’s being blocked by other other areas of pressure, east and west.”
Even less certain is whether the blocking, or ridging, pattern associated with heat domes are becoming more frequent. Some scientific literature points to this being the case, including a 2012 study that found slower patterns favoring extreme weather are becoming more common in mid-latitude regions.
A more recent study on the 2021 heat dome shows that climate change “is actually favoring the jet stream behavior that produces these stagnant high pressure systems and the extreme heat and drought associated with them,” said Michael Mann, one of the study’s authors and a presidential distinguished professor at the University of Pennsylvania, in an email. (The jet stream is the river of air that moves weather systems eastward across the globe).
Mann noted that heat domes aren’t just warm at the surface like heat waves, but have a deep layer of warm air and high pressure associated with sinking dry hot air. He said they’re the sort of air masses often associated with desert conditions — and with a particular jet stream pattern called an “omega block” because of its shape.
“Our work shows that climate models aren’t doing a good job yet in capturing this effect, meaning that the models are probably underestimating the impact that climate change is having on these persistent summer weather extremes (heat domes, heat waves, wildfires, as well as extreme flooding events),” he said.
And while the term “heat dome” has recently risen in prominence, Mann said it goes back nearly half a century. However, climate change is leading to increased incidents of the underlying conditions associated with such events, he said.
In fact, research has shown heat waves now occur three times as often as they did in the 1960s. Heat domes, like the one that smothered the Pacific Northwest in 2021, are also 150 times more likely due to climate change, another study found.
Climate change is also leading to warmer global temperatures and greater temperature extremes, Abatzoglou said, “so when events like this do occur, the temperatures along with them are substantially warmer.”
In some ways, then, the term heat dome is not unlike other meteorological phenomena that have gained prominence in recent years, including real terms such as atmospheric rivers and bomb cyclones, and more colorful terms such as firenadoes and hurriquakes.
Another recent coinage is the “ridiculously resilient ridge,” a phrase from UCLA climate scientist Daniel Swain used to describe a blocking pattern to the west of California in the winter months that deflects storms north of the region.
Abatzoglou said heat domes are somewhat similar, except that the ridge sets up over land with the jet stream often well to the north, and the ridge pattern gets “stuck.”
But extreme heat is particularly dangerous — among the deadliest of all extreme weather events — and often, the first heat wave of the year is the most impactful because people have not yet acclimated, Abatzoglou said. Sometimes, the most important task is accurately communicating that threat to the public.
“I’ve said these are ‘ridging events,’ and to many people that’s jargon and it doesn’t translate,” he said. “And so we have to go from talking about ‘500 millibar geopotential heights’ that a really small audience appreciates and understands, to something that captures the essence of the event. And this really is a large blocking.”
Science
Video: NASA Announces Artemis III Crew
new video loaded: NASA Announces Artemis III Crew
transcript
transcript
NASA Announces Artemis III Crew
NASA announced the crew of Artemis III mission, which will fly to low-Earth orbit to test rendezvous and docking maneuvers with one or two lunar landers.
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“I am excited to welcome you as the next crew in the Artemis journey to successfully return to the moon — this time to stay.” “I’m honored by the role that I’ve been given. I’m also very humbled by the task in front of us. But first and foremost, I’m grateful.” “So with that, the Artemis II crew, comrade, hands you the baton. You got the controls.” “As you know, we had a significant anomaly at our Launch Complex 36A on May 28. We’ve redoubled our efforts and are moving forward.”
By Alisa Shodiyev Kaff
June 9, 2026
Science
Santa Monica Mountains’ last steelhead trout survived the Palisades fire — and even had babies
Scientists feared the Santa Monica Mountains’ last remaining steelhead trout were dead, smothered by debris flows unleashed by the Palisades fire.
But the endangered fish surprised them: A team of biologists recently spotted 30 of the rare trout — and 21 babies — in Topanga Creek.
“There was a lot of happy dancing in the creek,” said Rosi Dagit, principal conservation biologist for the Resource Conservation District of the Santa Monica Mountains, which works with public and private landowners to conserve natural resources.
That’s because the steelhead here are endangered, at both the state and federal levels. Once, they swam in most streams of the Santa Monicas, but their numbers plummeted amid overfishing and coastal development. Increasingly frequent wildfire has further stressed their habitat. Topanga Creek, a biodiversity hot spot, is home to their last known population in the mountains that stretch from the Hollywood Hills to Point Mugu in Ventura County.
The trout that were spotted, including this one, are part of a distinct Southern California population that’s listed as endangered at the state and federal levels.
(RCDSMM Stream Team)
The California Department of Fish and Wildlife spearheaded a complex mission to rescue trout threatened by the Palisades fire that sparked in January 2025.
Time was of the essence. The fire hadn’t yet been fully contained. But rain was on the way, which would sweep massive amounts of sediment from the denuded hillsides into the water. Fish are often killed this way.
Crews stunned the fish with electricity, scooped them up in buckets, trucked them to a hatchery and ultimately moved them to Arroyo Hondo Creek in Santa Barbara County.
Within days, Topanga Creek was choked with mud. Some assumed the fish left behind were goners.
But in March, the conservation district’s team found four. The following month, when water conditions were clearer, they saw more.
“These fish continue to amaze me,” said Kyle Evans, environmental program manager for the state Department of Fish and Wildlife, who had seen the damage to the creek. “I had seen populations get wiped out in similar situations. So when I heard, I was thrilled.”
Evans surmises the fish that survived were in an area of the creek where less charred material and sediment were swept in.
“These fish likely hunkered down, were hiding under some rocks or places to try to get away from the main concentration of flow,” he said. “And luckily they weren’t buried.”
The ones that were spotted were fairly small, around 6 to 14 inches. Rainbow trout and steelhead trout are the same species, but with different lifestyles. If the fish remain in freshwater, they’ll be considered rainbows. However, they can migrate to the ocean and become steelhead, where they typically grow larger before returning to their natal waters to spawn.
Topanga Creek hasn’t fully recovered from the damage it sustained, but scientists say it’s looking better. Surveys last year were “so depressing,” Dagit said, with very few animals, and stretches that were essentially transformed into flat roads from all the sediment buildup. Some of the riparian canopy burned right down to the creek.
Then came 32 inches of rain over the last nine months, scouring out and moving sediment, creating deeper pools. Dagit said they recently found newt egg masses for the first time in years, as well as a few adult newts and many frogs. Plants that provide cover are starting to recover.
She provided photos comparing certain pools last year and this year, some dramatically transformed. In September 2025, the Shrine Pool could have been an overgrown hiking trail. This April, it was filled with shallow water.
The Shrine Pool in September 2025, left, and the same location in April 2026, right, with RCDSMM’s Isaac Yelchin donning a wetsuit.
(RCDSMM Stream Team)
Topanga Creek is home to another endangered fish, the small but hardy northern tidewater goby, often described as cute. Not long before the trout operation, Dagit led a rescue of hundreds of these fish too. Many were repatriated to the lagoon at the mouth of the creek in a moving ceremony last June.
There’s still the matter of what to do with the trout that were moved to Santa Barbara County last year. Evans would like to bring them home to the Santa Monicas at some point, but isn’t sure if it will happen. On one hand, they could bolster the small, genetically isolated surviving population. On the other, they might inadvertently bring in a disease or bacteria. There is some time to decide. Evans estimates the creek still needs to recover for two to three more years.
For now, the fish are functioning fine in their adopted creek. Experts worried the trauma wrought by the move would disrupt their spawning process, but they had babies that spring. This year, they spawned again.
Science
Pacifica pier cracks, another coastal casualty as seas continue to rise
The Pacifica Municipal Pier was shut down and taped off Thursday after city workers noticed cracks running through the landmark structure and concrete chunks falling into the ocean.
It’s just one of many coastal California structures that have recently crumbled under pressure from a rising and relentless ocean.
Officials from the small, beach city south of San Francisco said the pier was closed due to “cracking, separation, and displacement of the concrete walkway and structural elements.”
It will stay closed while structural engineers asses its safety.
Photos taken by city employees show a wide crack that runs from top to bottom and across the structure as well. Other photos show a large horizontal crack under the foundation of a small restaurant on the pier, the Chit Chat Cafe.
The cafe was also shut down.
This is not the first time the 53-year-old pier has shown signs of stress. In 2021, part of it was shut down after handrails along the edge collapsed. And in 2023, after a series of storms pummeled the Central California coast, damaging parts of the pier, the structure was partially closed for more than year.
Those same storms caused extensive damage in Aptos and Capitola, 70 miles south, where piers and waterfront infrastructure were swept away or damaged.
In 2024, a 150- to 180- foot section of the Santa Cruz wharf was ripped off by powerful waves.
At least 10 of the state’s dozens of coastal public piers were closed for part or all of 2024 due to structural damage sustained in winter storms since 2022. At least five others have longer-term upgrades planned to address structural issues.
“These things are costly to maintain,” said Zach Plopper, senior environmental director at Surfrider. “They are a part of our California coastal culture in many ways, but we’re going to need to reckon with, one, the state that they’re in, and two, the continuous and worsening threats they’re going to experience,”
He said most of the piers were constructed in the early 1900s, and they weren’t built to withstand decades of rough seas, storms and rising sea level.
“With this incoming El Niño, which is forecasted to be significant, and this marine heat wave we’re in the midst of, we’re kind of in uncharted waters as far as what this winter could bring in terms of storms and swells to the California coast, and we’re likely going to see a lot more damage,” he said. “Not just piers, but roads and other coastal infrastructure up and down the state.”
There was no storm in Pacifica earlier this week, so no single event could be blamed for the destruction.
However, a 2025 report from an outside engineering firm, GHD, found that several sections of the pier were in “poor” or “serious” condition, and they recommended closure before anticipated storms or events that could “subject the piles to high winds, swells and large waves.”
The firm found several areas of the pier where concrete was missing and rebar was exposed and corroding.
“The pier has continued to experience high winds and large waves in a harsh marine environment,” the engineers wrote in the report, noting that continuous exposure to seawater or marine spray was “detrimental” to the structure.
A 2023 city report estimated it would cost $19 million to repair.
That same year, a state law was enacted to require local governments along the California coast to plan for sea level rise in the coming decades.
Sea level has risen some 8 inches, on average, along the coast in the past 150 years, Plopper said, and researchers anticipate another foot in the next 25 years.
“We’re going to see profound shifts on our coastline, none that we have ever experienced before, and building static structures on the coast just doesn’t work all that well,” he said. “We’re going to have to make some really hard decisions.”
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