WASHINGTON (dpa-AFX) - U.S. meteorologists have warned that high humidity, limited cloud cover, and light winds could make temperatures feel higher than thermometer readings and increase the risk of heat-related illnesses, as a swath of the south-central United States is sweltering under a heat dome.
While the calendar indicated that astronomical summer was winding down, temperatures approached or exceeded 40 degrees Celsius in many of these regions in mid-September, NASA said.
More than 41 million people in the U.S. - about 12 percent of the population - were under a National Weather Service extreme heat advisory, extreme heat watch, or extreme heat warning earlier this week. The high temperatures spanned large portions of several states, such as Texas, Oklahoma, Arkansas, Missouri, and Tennessee.
Several locations set new daily high temperature records on September 15. These included Dallas, at 101ºF (38ºC), Memphis, at 99ºF (37ºC), and Nashville, at 100ºF (38ºC). The cities were all at least 12ºF warmer than normal that day, with Nashville breaking its daily-high record from 1927. The day before, Nashville also set a record-high minimum temperature of 75ºF (24ºC).
A weather phenomenon meteorologists call a heat dome was responsible for driving temperatures up across the region. A heat dome develops when an area of high pressure in the upper atmosphere pushes hot air toward the surface and traps it there. Heat domes put the brakes on convection and suppress clouds and precipitation. This allows sunlight to reach Earth's surface relatively unhindered and further elevate air temperatures.
The stretch of unseasonable temperatures follows the warmest June through August in the contiguous United States in a 132-year record, according to NOAA. The three-month period in 2026 was 0.4ºF warmer than the previous records, set in 1936 and 2021.
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