Why the Heat Dome Sizzling Texas Won’t Budge

Texas is no stranger to scorching summer heat, but even Texans are growing weary of a major “heat dome” that has parked itself over the region and will keep temperatures soaring to potentially deadly extremes in the state for the third week in a row.

Many areas in Texas have experienced days of triple-digit temperatures. On Sunday the National Weather Service (NWS) office for Austin and San Antonio said in a tweet that the city of Del Rio, Tex., on the border with Mexico, had seen eight straight days with daily record highs, all in the triple digits. In central Texas, San Angelo hit 112 degrees Fahrenheit on Sunday, easily topping that date’s previous record of 106 degrees F in 1994. “It’s hard to believe that just a week ago, 112° would’ve been our all-time record high and now it’s just another day of 110° heat to add to the count,” the NWS San Angelo office wrote on Twitter. (The city set an all-time high of 114 degrees F the previous week.)

This relentless, record-breaking heat wave bears all the hallmarks of what scientists expect to see with climate change: namely, heat events that are more intense, last longer and happen more frequently.

��️��️Here’s yet another way to say, “It’s been hot.” We’ve had excessive heat warnings for two weeks straight! We’ve broken several high temperature records and had incredibly high dewpoint values. �� #txwx #stxwx #ItsHot pic.twitter.com/rfm4rPkfBO

— NWS Corpus Christi (@NWSCorpus) June 26, 2023

The stifling temperatures that have been baking Texas and Mexico since early June are happening because of a high-pressure system—also called a ridge—which has “gotten entrenched, and it really hasn’t budged much,” says Andrew Quigley, a meteorologist at the NWS office for Austin and San Antonio. High-pressure systems feature sinking air, which compresses and becomes warmer. These systems also bring clear skies, letting through plenty of sunlight that further raises surface temperatures. When such a system gets stuck over an area, it’s called a “heat dome.” Another heat dome developed over the Pacific Northwest and Canada in late spring, helping fuel wildfires that have sent smoke down over large sections of the U.S.

So why has the current Texas heat wave dragged on for so long? Once a heat dome has dug in, it takes a big push from the jet stream or another relatively strong system higher up in the atmosphere to dislodge it—and “we just haven’t seen any sort of influences like that crossing this part of the country,” Quigley says. The latest guidance from forecast models suggests the heat may not budge until sometime after July 4.

And it isn’t just the heat—it’s also the humidity. Texas’s proximity to the Gulf of Mexico means there is abundant moisture in the air, and high humidity raises the heat index (a measure of what temperatures feel like to the human body). Many locations have seen a record number of hours with dangerously high heat index readings, according to the NWS. A significant chunk of Texas has experienced heat indexes in the 110s or 120s F. Corpus Christi, Tex., located on the Gulf of Mexico, saw the heat index reach 125 degrees F. The city has also seen 14 days in a row of excessive heat warnings. “We’ve far surpassed the most excessive heat warning days that we have had in a year,” says Penny Harness, a meteorologist at the NWS Corpus Christi office.

Even in a part of the country that is no stranger to sultry summers, this prolonged extreme heat is dangerous, particularly to people who work outside—such as construction workers and farm workers—as well as unhoused people, the very young, the elderly and those with certain medical conditions, such as heart disease and asthma. “It’s dangerous for people because you just don’t have that chance to recover if it’s just day after day” of extreme heat, Harness says.

In the U.S., the number of heat-related illnesses and fatalities has been increasing since the 1980s. Heat is deadlier than more fearsome-sounding weather events such as hurricanes, floods and tornadoes—combined. “It’s really not even close with any other extreme,” says Greg Carbin, chief of forecast operations at the NWS’s Weather Prediction Center.

NWS offices and other officials across Texas have been warning residents to limit strenuous outdoor activity, to take plenty of breaks (ideally indoors with air-conditioning or at least in the shade) if working outdoors and to frequently drink plenty of water. “If you’re feeling thirsty,” Quigley says, “it’s already too late.”

Climate change is amplifying this and other heat events, as global average temperatures are already about two degrees F (one degree C) higher than in preindustrial times. With the planet still warming as humans continue to burn fossil fuels that release heat-trapping greenhouse gases, heat waves will continue to happen more often, last longer and reach higher temperatures. In part because of more extreme heat waves, an unusually hot summer in the past is now considered average. And today’s record hot summers will seem ho-hum in the future if we do not significantly curtail greenhouse gas emissions.

There is also some research that suggests climate change may be increasing the likelihood of weather patterns like this sticking in place. The idea is that the rapid warming of the Arctic is altering the jet stream—the fast-moving current of air that guides weather systems around the Northern Hemisphere—in a way that makes these weather patterns stick in place.

In the coming days, the heat dome over Texas may shift slightly, bringing hotter weather to some surrounding states. “There’s not much of a break in sight,” Carbin says.

Eventually the pattern will dislodge—though that does not seem likely until sometime next week—and temperatures in Texas will drop back to the more seasonable upper 90s, which absurdly “will be some sense of relief,” Quigley says.