A dome of exceptionally warm late-season air hovers over the eastern third of the nation, bringing temperatures more than 20 degrees above average. (WeatherBell.com)

Over the past week, extreme heat has visited more than 130 million Americans, shattering temperature records for this time of year with readings that would be impressive even by July standards. Although temperatures have dropped on Thursday across the Northeast and Mid-Atlantic, the atmospheric blowtorch remains lit for folks in the Southeast and the Deep South.

The records

  • Wednesday’s high of 98 degrees in Wilmington, Del., didn’t just set an October record — it was their warmest reading of any month since 2012.
  • Atlantic City hit 96 degrees on Wednesday, clinching its new October record by an impressive margin of six degrees. Newark also set a new monthly record at 96 degrees. John F. Kennedy International and LaGuardia airports smashed October records, as well.
  • In the Washington region, Reagan National Airport soared to 98 degrees, its warmest October reading on record, beating a record that had stood since 1941. Highs ran more than 25 degrees above normal.
  • Tallahassee set its October record, as did Atlanta. Atlanta wrapped up September almost nine degrees above average.
  • Chattanooga, Tenn., hit 100 degrees on Wednesday, breaking the October record it had set just one day prior, at 97 degrees. Before this year, it had never hit 95 degrees or above this late in the year. Nashville, Memphis, and Knoxville also set record highs for the month of October.
  • Averaged over the past week, Huntsville, Ala.; Birmingham, Ala.; Tallahassee; New Orleans; and Atlanta have all been hotter than Death Valley, Calif., which holds the all-time heat record for the United States.

For many, this heat is nothing new. Nashville was above average every day in September. Like Atlanta, it hasn’t had a single below-average day since the end of August. That means that every day in meteorological fall (the months of September, October and November) has featured anomalously hot weather.

A measurement mystery

In Alabama, Jasper recorded a high of 104, while Birmingham hit 103 degrees. The former could mark the warmest October temperature recorded in any state east of the Mississippi, according to Bill Karins, an NBC News meteorologist. But the National Weather Service in Birmingham warned that both records appeared suspect.

“The [temperature] rose from 97 degrees to over 100 degrees, back down, back up, & back down, in just a few minutes” in Birmingham, the office wrote on Twitter.

“These were very considerable temperature swings over a very short time, so that makes it questionable right now,” Tara Goggins, a forecaster there, said in an interview.

Jasper, the site that purportedly hit 104, also has a “history of running warm,” Goggins said. On Twitter, the office cited a “longstanding warm bias.”

Neither weather station is maintained by the National Weather Service, because the Federal Aviation Administration is responsible for calibrating and servicing the Birmingham sensor, which is located at that city’s airport.

It’ll be up to the National Centers for Environmental Information, which oversees and verifies all climate extremes, to determine whether to count these suspicious readings.

Elsewhere in Alabama, Tuscaloosa and Huntsville did set records that meteorologists are more confident about — reaching 101 and 100 degrees, respectively.

The climate context

The persistent heat across the Southeast is noteworthy and does not show signs of dissipating soon. In addition, one of the most robust findings of climate science research is that long-term, human-caused climate change is raising the odds of heat waves and boosting their severity and duration. Studies examining specific extreme heat events, such as two European heat waves in the summer, have found clear fingerprints of global warming on many of them.

For example, a study on a 2018 heat wave in Japan found the event could not have occurred in the absence of a warming climate. As the climate continues to warm, more of these expansive late-season heat waves can be expected, as the cool season shrinks in length.

While temperature extremes on both ends of the spectrum will still occur, the scale is being disproportionately tilted in favor of warm records rather than cold.

Andrew Freedman contributed to this report.