Heatwave: Vicious ‘heat dome’ toasts California

The extreme temperatures that will weigh on California over the next week are the result of a “heat dome,” a phenomenon that typically brings toasty conditions to the state as summer turns into fall. But climate change is worsening the effects of the dome and making it deadlier for people who cannot seek help.

Experts are sounding the alarm over what they say will be the worst heat wave of the year so far.

“We’ve always had these systems, but not as frequently, not as intense, and not as long-lasting,” said Bill Patzert, a retired Los Angeles-area climatologist.

From San Diego to Sacramento, the National Weather Service issued an excessive heat warning or watch over Labor Day, warning of the risk for the health sustained high temperatures. Experts say the heat wave will also increase the risk of wildfires and power outages and exacerbate the state’s current drought.

“It’s going to be a long-lasting event,” said UCLA climatologist Daniel Swain. “And that’s sort of a characteristic of heated domes – it’s partly because they can kind of be self-persistent, self-reinforcing. Once they grow and get particularly extreme, they become somewhat difficult to dislodge.

What is a heated dome?

Swain said “heat dome” is a colloquial term for “a region of particularly persistent and strong high atmospheric pressure during warm months.”

As the high pressure system moves through an area under certain conditions, it retains heat, like an insulated dome. This is what will bring extreme temperatures this week across California and Nevada.

“When you’re inside a high-pressure system, especially a powerful system, you usually have downward motion in the atmosphere, as opposed to upward motion…and that removes the clouds,” Swain said. . “This results in clear skies, so you get more solar radiation, more surface heating.

“But beyond that…you get additional warming, because that downward motion itself results in compressive heating.”

He called these simultaneous effects the “vicious circle feedbacks” of the thermal dome: heat dries out the ground, which removes atmospheric moisture, which makes it easier for the sun to heat the Earth’s surface, and so on.

“You can kind of see how it’s perpetuated,” Swain said. “And that’s what we’re going to see this week into next week over California and Nevada. We’re going to see this persistent high pressure system – it’s a pretty extreme heat dome – which is going to accumulate more and more heat as it persists through these processes.

Heat waves become deadliest and most common in the Golden State. A recent study analyzing data from 1950 to 2020 found that heat waves in Southern California “began earlier and ended later in the year for urban areas”, a trend that is “linked to human-induced climate change”.

Glynn Hulley, a researcher at NASA’s Jet Propulsion Laboratory who led the study, said his team found heat waves had become “more frequent, more intense and longer lasting”. He said this week’s heat wave fell into the “more intense” category, with record high temperatures expected.

“It’s the intensity of it that matches the trends we’re seeing,” Hulley said.

While climate change doesn’t cause heat domes, he said, contributing factors — like extreme drought and a warmer atmosphere — make the effect more extreme.

“Every year we tend to break more and more records — not just in Los Angeles but across the planet,” Patzert said. “I don’t call it global warming anymore; I call it global warming.

Where to expect extreme heat

The National Weather Service predicts that from Wednesday through Labor Day weekend, temperatures could reach 115 degrees in parts of Southern California. It will be the longest and most intense heat wave of the year in the region, said David Sweet, meteorologist with the National Weather Service in Oxnard. Conditions are expected to last through Monday, although “we don’t see an end to it yet,” Sweet said.

An excessive heat warning is in effect from 11 a.m. Wednesday to 8 p.m. Monday in much of Southern California, including Los Angeles County, Ventura County and southern coastal Santa Barbara County.

For Riverside, Orange and San Bernardino counties, the warning takes effect at 10 a.m. Tuesday and lasts until 8 p.m. Monday.

“Generally, Wednesday through Monday, any of these days in the valleys, mountains, foothills and deserts – especially in the valleys and deserts – we can see peaks [above 110]“Sweet said.

Temperatures in Woodland Hills could reach 105 on Thursday and reach 110 on Sunday. Lancaster in the Antelope Valley could hit 108 on Thursday and Sunday. In Santa Clarita, Newhall could hit 106 on Thursday and 108 on Sunday.

“The entire state is likely to be very hot away from the immediate beaches, and it could even be very hot there,” Swain said. “But I think the most relatively extreme temperatures and relative to historical averages are likely to be in the interior, central and northern California: the San Joaquin and Sacramento Valleys…and the eastern Bay of San Francisco.”

Dangerous heat

Such heat can be extremely dangerous, especially when temperatures don’t drop at night and allow the body to recover from the scorching peaks of the day.

“We often focus on high temperatures during the day – you know, 100, 110, 115 degrees,” Swain said. “And, of course, these can have major impacts. But it’s often when heat waves don’t cool at night that actually cause the most cumulative damage to human health and ecosystems.

A Times investigation published last year revealed that California has done a poor job of tracking the number of people who have died from extreme heat and has largely failed to provide resources to communities most vulnerable to the effects of heat and global warming. In January, the administration of Governor Gavin Newsom announced a plan to cope with oppressive heat which includes recommendations on how to monitor deaths caused by heat waves and the possible establishment of temperature limits for residential units.

Extreme temperatures can increase the risk heat-related illnesses, from skin rashes to heat exhaustion or heat stroke. Children, the elderly and people living with limited resources are particularly vulnerable. The National Weather Service and public health units are advising people to stay indoors as much as possible during the extreme heat – especially between 10 a.m. and 3 p.m.when the sun is strongest – and to stay well hydrated and use air conditioning when possible.

“This is one of the fastest warming times of the year in California, from a climate change perspective,” Swain said. “You could say that September becomes a summer month. … I think we’re really seeing that manifesto this year, where we’re going to start the month with record heat – and there’s every indication that the rest of the month will probably be even hotter than average.

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