What’s a heat dome? Here’s why Texas heat is expected to spread.

Scorching temperatures from a heat dome are taxing the Texas power grid, threatening to bring record highs to the state before expanding to other parts of the United States. Experts say more than 46 million Americans are under heat alerts.

First Look

Scorching temperatures brought on by a “heat dome” have taxed the Texas power grid and threaten to bring record highs to the state before they are expected to expand to other parts of the United States during the coming week, putting even more people at risk.

“Going forward, that heat is going to expand ... north to Kansas City and the entire state of Oklahoma, into the Mississippi Valley ... to the far western Florida Panhandle and parts of western Alabama,” while remaining over Texas, said Bob Oravec, lead forecaster with the National Weather Service.

Record high temperatures around 110 degrees Fahrenheit are forecast in parts of western Texas on Monday, and relief is not expected before the Fourth of July holiday, Mr. Oravec said.

Cori Iadonisi, of Dallas, summed up the weather simply: “It’s just too hot here.”

Ms. Iadonisi said she often urges local friends to visit her native Washington state to beat the heat in the summer.

“You can’t go outside,” Ms. Iadonisi said of the hot months in Texas. “You can’t go for a walk.”

What is a heat dome?

A heat dome occurs when stationary high pressure with warm air combines with warmer than usual air in the Gulf of Mexico and heat from the sun that is nearly directly overhead, Texas State Climatologist John Nielsen-Gammon said.

“By the time we get into the middle of summer, it’s hard to get the hot air aloft,” said Mr. Nielsen-Gammon, a professor at Texas A&M’s College of Atmospheric Sciences. “If it’s going to happen, this is the time of year it will.”

Mr. Nielsen-Gammon said July and August don’t have as much sunlight because the sun is retreating from the summer solstice, which was Wednesday.

“One thing that is a little unusual about this heat wave is we had a fairly wet April and May, and usually that extra moisture serves as an air conditioner,” Mr. Nielsen-Gammon said. “But the air aloft is so hot that it wasn’t able to prevent the heat wave from occurring and, in fact, added a bit to the humidity.”

High heat continues this week after it prompted Texas’ power grid operator, the Electric Reliability Council of Texas, to ask residents last week to voluntarily cut back on power usage because of anticipated record demand on the system.

The National Integrated Heat Health Information System reports more than 46 million people from west Texas and southeastern New Mexico to the western Florida Panhandle are currently under heat alerts. The NIHHIS is a joint project of the federal Centers for Disease Control and Prevention and the National Oceanic and Atmospheric Administration.

The heat comes after Sunday storms that left more than 100,000 customers without electricity in both Arkansas and Tennessee and tens of thousands powerless in Georgia, Mississippi, and Louisiana, according to poweroutage.us.

Earlier this month, the most populous county in Oregon filed a $1.5 billion lawsuit against more than a dozen large fossil fuel companies to recover costs related to extreme weather events linked to climate change, including a deadly 2021 heat dome.

Multnomah County, home to Portland and known for typically mild weather, alleges the combined carbon pollution the companies emitted was a substantial factor in causing and exacerbating record-breaking temperatures in the Pacific Northwest.

An attorney for Chevron Corp., Theodore J. Boutrous Jr., said in a statement that the lawsuit makes “novel, baseless claims.”

What are the health threats?

Extreme heat can be particularly dangerous to vulnerable populations such as children, the elderly, and outdoor workers who need extra support.

Cecilia Sorensen, a physician and associate professor of Environmental Health Sciences at Columbia University Medical Center, said heat-related conditions are becoming a growing public health concern because of the warming climate.

“There’s huge issues going on in Texas right now around energy insecurity and the compounding climate crises we’re seeing,” Ms. Sorensen said. “This is also one of those examples where, if you are wealthy enough to be able to afford an air conditioner, you’re going to be safer, which is a huge climate health equity issue.”

In Texas, the average daily high temperatures have increased by 2.4 degrees – 0.8 degrees per decade – since 1993, according to data from the National Oceanic and Atmospheric Administration amid concerns over human-caused climate change resulting in rising temperatures.

This story was reported by The Associated Press. Ken Miller reported from Oklahoma City, Oklahoma, and Isabella O’Malley reported from Philadelphia, Pennsylvania.