Heat advisories stretch from northern Florida to southern New Mexico, and excessive-heat warnings have been issued for much of Texas and parts of New Mexico and Arizona and along the Gulf Coasts of Louisiana, Mississippi and Alabama. New Orleans is included in the zone of greatest heat risk, with actual air temperatures around 100 degrees and humidity that will push heat indexes to 115 degrees.
Excessive-heat watches, meanwhile, have been posted for the lower Mississippi Valley and include Memphis and Nashville; Huntsville and Birmingham, Ala.; Jackson, Miss., Little Rock; and Poplar Bluff, Mo.
Instigating the heat has been a stagnant ridge of high pressure parked over Texas. That “heat dome” brought hot, sinking air while deflecting storm systems around it to the north. The uninterrupted sunshine helped temperatures to spike by 8 degrees to 18 degrees above average.
What set this heat dome apart was not just its magnitude, however. Its stubbornness and longevity also have been big factors in its anomalous impacts. The city of Del Rio, Tex., hit 115 degrees June 21, for instance, and could reach a 10th consecutive day of tying or breaking record highs.