Cooling trend coming after week under oppressive 'heat dome'

Aug. 24—A "heat dome" in recent days over a large portion of the central U.S. is being cited for some of the highest heat index readings ever in the region, but forecasters are saying that some relief could be in sight over the weekend.

Temperatures this week in Joplin have topped out daily in the upper 90s and low 100s, and unusually high humidity has created some of the highest heat index readings ever recorded at the Springfield National Weather Service station.

Justin Titus, a meteorologist with the weather service, said a "heat dome" over a large section of the country prompted the weather service to issue excessive heat warnings and watches across parts of 20 states, including all of Missouri and Arkansas, and the eastern counties of Kansas and Oklahoma.

"It was unofficially one of the strongest high-pressure centers we've ever seen over the area," Titus said. "High pressure means clear skies. We get a lot of sun, (and) you see sinking air in high pressure, so you get that additional warming from that as well."

Titus said heat index readings, which measure how the air feels on the human body by combining the air temperature and relative humidity, topped out over 120 degrees in Joplin on several days recently. He said the heat index Monday in Joplin hit 124 degrees.

"Normally we don't see this sort of really hot temperatures in the mid- to upper 90s to over 100 combined with the humidity," Titus said. "Normally in this area, we don't get that hot unless it's really dry. We had a lot of rain in the week before this past week, and the vegetation is green and pumping out a lot of moisture. Also there's a good amount of moisture in the atmosphere now, and that combination of the high heat and high humidity is giving us these heat index values that are rarely seen around here."

Titus said one aggravating factor is the lack of nighttime cooling during this period of heat advisories. Temperatures on Tuesday and Wednesday night cooled to a still-warm 80 degrees, and temperatures bottomed out in the mid-70s for three nights before that.

"That's a big health hazard with heat events," Titus said, adding, "Some people might not have good air conditioning or none at all, and you can't recuperate at night, and it compounds the risk for health problems."

Heat in the Midwest

Heat warnings and advisories have been in place this week from New Orleans to Minneapolis, leading to some deadly results. Just this week, a 1-year-old left in a hot van in Nebraska died, and Louisiana reported 25 heat-related deaths this summer — more than twice the average number in recent years.

Cities in Texas and Louisiana have recorded heat index readings higher than 110 more often than at any time since World War II, said Alex Lamers, a warning coordination meteorologist at the National Weather Service's Weather Prediction Center.

As a result, cooling systems are under strain. Missouri firefighters helped remove 117 patients from a Kansas City nursing facility Tuesday after its air conditioning failed. The heat index at the time was 115 degrees. Most Parkview Healthcare nursing facility residents were taken to other facilities, authorities said.

Students across the U.S. were back in school this week. The heat prompted officials in some districts, including Denver, to cut back on the length of the school day Wednesday. Chicago-area schools delayed classes or ended them early. Milwaukee Public Schools, Wisconsin's largest, closed campuses through Thursday.

Experts also have warned that infrastructure can be damaged under the extreme strain of enduring and recurring heat waves brought on by climate change. Costs in the U.S. for road maintenance and replacement due to rising temperatures could reach $26.3 billion by 2040, with most of the damage expected to hit Texas, California and Illinois, according to a 2017 study by University of Arizona and Arizona State University researchers.

'Quite a bit cooler'

Titus said the region could see a break in the heat over the weekend.

The high is predicted to reach 99 on Friday, 92 on Saturday, then only 83 with a slight chance of showers on Sunday. Low temperatures are expected to drop to a much more comfortable 66 degrees Sunday night, 63 on Monday night and 58 on Tuesday night.

"It's going to be hot out there, but not as hot this weekend. Then going into the early part of next week, especially Monday and on, it's looking quite a bit cooler," Titus said. "We're at least through the peak of this event. It may get a little warmer starting the first week of September, but we're likely not to get that hot again."

Titus said residents need to continue to be aware of the dangers of heat for a few more weeks.

"We could still see heat indexes of 100 at times; that still causes problems," he said. "It's just not as bad as 125. Just be aware we're still in summertime. We can get hot conditions through the whole summer in the Ozarks, and we need to be aware of the safety related to that."

The Associated Press contributed to this report.