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.”
The sun had barely risen over the Pacific Ocean when a small motorboat carrying a team of Indigenous artisans and Mexican biologists dropped anchor in a rocky cove near Bahías de Huatulco.
Mauro Habacuc Avendaño Luis, one of the craftsmen, was the first to wade to shore. With an agility belying his age, he struck out over the boulders exposed by low tide. Crouching on a slippery ledge pounded by surf, he reached inside a crevice between two rocks. There, lodged among the urchins, was a snail with a knobby gray shell the size of a walnut. The sight might not dazzle tourists who travel here to see humpback whales, but for Mr. Avendaño, 85, these drab little mollusks represent a way of life.
Marine snails in the genus Plicopurpura are sacred to the Mixtec people of Pinotepa de Don Luis, a small town in southwestern Oaxaca. Men like Mr. Avendaño have been sustainably “milking” them for radiant purple dye for at least 1,500 years. The color suffuses Mixtec textiles and spiritual beliefs. Called tixinda, it symbolizes fertility and death, as well as mythic ties between lunar cycles, women and the sea.
The future of these traditions — and the fate of the snails — are uncertain. The mollusks are subject to intense poaching pressure despite federal protections intended to protect them. Fishermen break them (and the other mollusks they eat) open and sell the meat to local restaurants. Tourists who comb the beaches pluck snails off the rocks and toss them aside.
A severe earthquake in 2020 thrust formerly submerged parts of their habitat above sea level, fatally tossing other mollusks in the snail’s food web to the air, and making once inaccessible places more available to poachers.
Decades ago, dense clusters of snails the size of doorknobs were easy to find, according to Mr. Avendaño. “Full of snails,” he said, sweeping a calloused, violet-stained hand across the coves. Now, most of the snails he finds are small, just over an inch, and yield only a few milliliters of dye.
new video loaded: This Parrot Has No Beak, But Is at the Top of the Pecking Order
By Meg Felling and Carl Zimmer
April 20, 2026
For months now, menopausal women across the U.S. have been unable to fill prescriptions for the estradiol patch, a long-established and safe hormone treatment. The news media has whipped up a frenzy over this scarcity, warning of a long-lasting nationwide shortage. The problem is real — but the explanations in the media coverage miss the mark. Real solutions depend on an accurate understanding of the causes.
Reporters, pharmaceutical companies and even some doctors have blamed women for causing the shortage, saying they were inspired by a “menopause moment” that has driven unprecedented demand. Such framing does a dangerous disservice to essential health advocacy.
In this narrative, there has been unprecedented demand, and it is explained in part by the Food and Drug Administration’s recent removal of the “black-box warning” from estradiol patches’ packaging. That inaccurate (and, quite frankly, terrifying) label had been required since a 2002 announcement overstated the link between certain menopause hormone treatments and breast cancer. Right-sizing and rewording the warning was long overdue. But the trouble with this narrative is that even after the black-box warning was removed, there has not been unprecedented demand.
Around 40% of menopausal women were prescribed hormone treatments in some form before the 2002 announcement. Use plummeted in its aftermath, dipping to less than 5% in 2020 and just 1.8% in 2024. According to the most recent data, the number has now settled back at the 5% mark. Unprecedented? Hardly. Modest at best.
Nor is estradiol a new or complex drug; the patch formulation has existed for decades, and generic versions are widely manufactured. There is no exotic ingredient, no rare supply chain dependency, no fluke that explains why women are suddenly being told their pharmacy is out of stock month after month.
The story is far more an indictment of the broken insurance industry: market concentration, perverse incentives and the consequences of allowing insurance companies to own the pharmacy benefit managers that effectively control drug access for the majority of users. Three companies — CVS Caremark, Express Scripts and OptumRx — manage 79% of all prescription drug claims in the United States. Those companies are wholly owned subsidiaries of three insurance behemoths: CVS Health, Cigna and UnitedHealth Group, respectively. This means that the same corporation that sells you your insurance plan also decides which drugs get covered, at what price, and whether your pharmacy can stock them. This is called vertical integration. In another era, we might have called it a cartel. The resulting problems are not unique to hormone treatments; they have affected widely used medications including blood thinners, inhalers and antibiotics. When a low-cost generic such as estradiol — a medication with no blockbuster profit margins and no patent protection — runs into friction in this system, the friction is not random. It is structural. Every decision in that chain is filtered through the same corporate profit motive. And when the drug in question is an off-patent estradiol patch that has negligible profit margins because of generic competition but requires logistical investment to keep consistently in stock? The math on “how much does this company care about ensuring access” is not complicated.
Unfortunately, there is little financial incentive to ensure smooth, consistent access. There is, however, significant financial incentive to steer patients toward branded alternatives, or simply to let supply tighten — because the companies aren’t losing much profit if sales of that product dwindle. This is not a conspiracy theory: The Federal Trade Commission noted this dynamic in a report that documented how pharmacy benefit managers’ practices inflate costs, reduce competition and harm patient access, particularly for independent pharmacies and for generic drugs.
Any claim that the estradiol patch shortage is meaningfully caused by more women now demanding hormone treatments is a distraction. It is also misogyny, pure and simple, to imply that the solution to the shortage is for women’s health advocates to dial it down and for women to temper their expectations. The scarcity of estradiol patches is the outcome of a broken system refusing to provide adequate supply.
Meanwhile, there are a few strategies to cope.
- Ask your prescriber about alternatives. Estradiol is available in multiple formulations, including gel, spray, cream, oral tablet, vaginal ring and weekly transdermal patch, which is a different product from the twice-weekly patch and may be more consistently available depending on manufacturer and region.
- Consider an online pharmacy. Many are doing a good job locating and filling these prescriptions from outside the pharmacy benefit manager system.
- Call ahead. Patch shortages are inconsistent across regions and distributors. A call to pharmacies in your area, or a broader geographic radius if you’re able, can locate stock that your regular pharmacy doesn’t have.
- Consider a compounding pharmacy. These sources can sometimes meet needs when commercially manufactured products are inaccessible. The hormones used are the same FDA-regulated bulk ingredients.
Beyond those Band-Aid solutions, more Americans need to fight for systemic change. The FTC report exists because Congress asked for it and committed to legislation that will address at least some of the problems. The FDA took action to change the labeling on estrogen in the face of citizen and medical experts’ pressure; it should do more now to demand transparency from patch manufacturers.
Most importantly, it is on all of us to call out the cracks in the current system. Instead of repeating “there’s a patch shortage” or a “surge in demand,” say that a shockingly small minority of menopausal women still even get hormonal treatments prescribed at all, and three drug companies control the vast majority of claims in this country. Those are the real problems that need real solutions.
Jennifer Weiss-Wolf, the executive director of the Birnbaum Women’s Leadership Center at New York University School of Law, is the author of the forthcoming book “When in Menopause: A User’s Manual & Citizen’s Guide.” Suzanne Gilberg, an obstetrician and gynecologist in Los Angeles, is the author of “Menopause Bootcamp.”
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