Predicted heat indexes in the southern part of Texas on Saturday afternoon by the National Weather Service.

Parts of Texas and southern Louisiana are feeling like a steam room amid a dangerous heat wave that’s set to last more than a week. Blistering heat and stifling humidity have already combined to push the heat index above 120 degrees in spots, posing a significant danger to vulnerable populations and those without adequate access to cooler environments.

The Lone Star State broke heat records on Thursday and Friday, and many more are expected to fall over the coming days.

Texas Gov. Greg Abbott (R) said at a news conference Saturday that he spoke with the Electric Reliability Council of Texas, the organization that operates the state’s electrical grid, ahead of the heat wave. Officials there assured him they could meet what “may be a record power demand” as Texas residents try to cool their homes, Abbott said.

Excessive heat warnings and heat advisories affect more than 40 million people this weekend. The warnings, which are the most dire type of heat alert the National Weather Service issues, extend from the border of Mexico and southwest Texas to the border of southern Louisiana and Mississippi. Population centers in the warning zone include Brownsville, Corpus Christi, Austin, San Antonio, Houston, Galveston and Lufkin in Texas and New Orleans, Baton Rouge and Alexandria in Louisiana.

“Extreme heat and humidity will significantly increase the potential for heat related illnesses, particularly for those working or participating in outdoor activities,” the National Weather Service cautioned.

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Heat advisories, for somewhat lesser heat, cover the Texas Big Bend and Edwards Plateau and include San Angelo, the Dallas-Fort Worth Metroplex and into northwest Louisiana.

Especially concerning is that the tropical humidity will trap heat overnight, preventing nightly lows from dipping below 80 degrees in spots.

“Daily record warm minimum temperatures … will compound the effects of the heat wave,” the Weather Service wrote. There exists a strong link between premature deaths of individuals with preexisting vulnerabilities or health complications and warm overnight temperatures, which can prevent the body from cooling down at night.

The exceptional heat and humidity have fueled severe thunderstorms farther to the north over North Texas, Oklahoma, the lower Mississippi Valley and parts of the Deep South. More than 800 reports of severe weather were received by the Storm Prediction Center between Wednesday and Thursday alone. A deadly tornado, rated EF3 on the 0 to 5 Enhanced Fujita scale, killed three people in the town of Perryton, located in the Texas Panhandle, while hail approximately 6 inches in diameter — bigger than a DVD — bombarded the town of Sanger, northwest of Dallas.

“I’ve seen more tornadoes than I can count. I’ve never seen the level of decimation to a town, as I’ve seen today,” Abbott said at a news conference in Perryton on Saturday. He promised state funds through a disaster declaration he signed this weekend.

An estimated 150,000 customers are without power in the far northeast counties of Texas after the violent storms tore through the area Thursday night, according to the tracking site Poweroutage.us. The state’s power grid may also be strained by the prolonged heat wave.

In the past year, Texas has hit 11 all-time records for power demand, but the grid was able to accommodate electricity needs “with ease,” Abbott assured residents Saturday. He said more power has been added to the grid since last summer, when ERCOT officials had to call on Texas residents to voluntarily limit their energy demand by reducing use of cooling systems like air conditioners.

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The state’s grid will be able “to summon the power that’s going to be needed to ensure that there will be no shortage of power this summer,” Abbott said.

Abbott’s comments on the state’s energy grid offer a more hopeful perspective than statements made by Texas Public Utility Commission Chair Peter Lake. In May, Lake said Texas’s main power grid was still at risk for outages if wind turbines were not able to produce enough electricity when it’s needed the most, according to the Texas Tribune.

Why it’s so hot

It doesn’t take a meteorologist to predict that it’s going to be hot in Texas during the summer months, but temperatures have been running 8 to 12 degrees above average and contributing to dangerous heat index values, which take into account both temperature and humidity. The scorching conditions are linked to a heat dome, or a ridge of high pressure, centered over northern Tamaulipas, Mexico.




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Heat domes bring hot, sinking air. They act as force fields, deflecting the jet stream and inclement weather to the north. That’s why thunderstorms have been plaguing North Texas, but leaving South Texas alone.

The pattern is highly unusual since, most summers, a heat dome (often called a “death ridge” by storm chasers) is parked over the Plains. This year, it’s been suppressed south by an unusual jet stream pattern that’s split the jet stream. The southern branch, also known as the “subtropical jet,” has been draped over the southern United States, which is contributing to severe weather.




© WeatherBell
A stagnant heat dome languishes over northern Mexico.

South of the jet and beneath the heat dome, however, there’s nothing to interrupt the sweltering heat that’s built up. And with weak winds around the high, Gulf of Mexico moisture has wafted northward, turning the atmosphere into a veritable steam bath.

How hot it will get




© WeatherBell
Air temperatures Monday afternoon as predicted by the National Weather Service. Boxed values are predicted records. (WeatherBell)

The National Weather Service is calling for “widespread record to near-record daytime heat with temperatures into the 100s” with heat indexes up to 120 the next several days. A few spots could set heat records for the entire month of June, it noted.

The triple digit temperatures will stretch from the Texas Gulf Coast, and reach a maximum of around 110 to 114 degrees farther inland around Laredo and Zapeta in the Rio Grande Valley. Austin should be between 103 and 106 for daytime highs through the midweek, except next Thursday, it’s forecast to hit 107 degrees.

In Houston, highs in the lower 100s are forecast through Tuesday, with a high of 100 degrees anticipated Wednesday. Thereafter, the heat will ease only slightly. And with Houston’s characteristic humidity, heat indexes as high as 117 degrees remain possible.




© WeatherBell
Forecast heat indexes across Texas on Monday afternoon.

Dallas will inch toward 100 degrees, but the humidity will make it feel like it’s 105 to 110 degrees outside.

New Orleans will see air temperatures in the mid- to upper-90s through Tuesday, but heat indexes across southeast Louisiana could push toward 114 degrees.

How long the heat will last

Excessively hot conditions are forecast through at least June 25.

Signs point to the heat beginning to break down toward late next week. That will come as the position of the heat dome inches west a little bit, putting Texas in line for a more southerly flow. That in turn will draw more moisture north over the Lone Star State, which will keep overnight temperatures near record warm levels, but it should prevent actual daytime highs from getting quite as hot. Still, heat index values will linger at dangerous levels for many as high humidity remains entrenched.

How hot and humid it’s been already

Heat and humidity gradually increased over the last several days and were particularly intense late in the workweek.

On Thursday, Kingsville, Tex., about 35 miles southwest of Corpus Christi, registered a heat index of 125 degrees. That same day, Dallas matched its highest dew point, an indicator of humidity, on record of 80 degrees. (That means that, if the air temperature had cooled to 80 degrees, the relative humidity would have been 100 percent.)

Heat indexes around Houston soared to between 110 and 120 degrees both Thursday and Friday.

On Friday, Junction, Tex., about 120 miles west of Austin, hit 110 degrees, its all-time high.

Record-breaking heat has extended south of the border into Mexico. On Thursday, Mexico City hit 92.5 degrees — its highest June temperature on record. That may not sound that high, but it sits at an elevation of over 7,000 feet.

A ‘heat burst’ in Central Texas

Imagine reaching nearly 100 degrees in the middle of the night! That’s what happened in Georgetown, a city in Central Texas, on Friday night.

At midnight, the temperature was 82 degrees, but it lurched to 99 degrees just over an hour later. Humidity plummeted at the same time.

What happened? A dying thunderstorm abruptly collapsed, causing a plume of air to rush down toward the ground. As air subsides toward the surface, it warms. That plume of air evidently began to dry out at the same time, which made it denser than the surrounding air, causing it to accelerate toward the surface even more quickly. That delivered a very hot, bone-dry wind that caused temperatures to skyrocket.

Climate change connections

The scientific literature is replete with studies connecting the increasing intensity, frequency, duration and size of heat waves to human-caused climate change.

Climate Central, a nonprofit science communication organization based in Princeton, N.J., has developed the Climate Shift Index, which estimates how much climate change is increasing the likelihood of extreme heat. The index is at a Level 5 over southern portions of Texas and southwest Louisiana, indicating that “human-caused climate change made this excessive heat at least 5 times more likely,” it said in a news release.