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.
“Extreme heat and humidity will significantly increase the potential for heat related illnesses,” cautioned the National Weather Service, “particularly for those working or participating in outdoor activities.”
The heat will relent somewhat into early next week for portions of the Southeast and Mid-South, but there is no immediate end in sight for Texas, where blistering and brutal conditions look to continue.
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.
Even more noteworthy have been the overnight lows in the city, which haven’t dipped below 80 degrees since the morning of June 15. The average low in Del Rio during mid- to late June is 74 degrees, but increased humidity — the same that is contributing to hazardous daytime heat indexes — is generating warm overnight lows. That is especially problematic, because high nighttime temperatures prevent the body from achieving its needed nocturnal cool-down.
Soupy humidity will continue to waft north out of the Gulf of Mexico. Dallas already logged an 80-degree dew point June 15, tying its record; this mark has been reached only five times since 1947. That oppressive sultriness will overlap with the heat until the overarching weather pattern finally breaks up late in the weekend.
The heat is also about to expand into the Mississippi Valley. So, although Texas will experience continued highs of between 100 degrees for places including Houston, San Antonio and Austin and lower 100s in Dallas and as high as 110 degrees in San Angelo, the worst is soon to spread north and east.
Oklahoma City will experience a brief flare-up of heat. Highs are likely to touch 105 degrees Tuesday and settle back into the lower 100s Wednesday. That would tie the record of 105 set in 1980.
New Orleans may not crack 100 degrees for the actual air temperature, but tropical rainforest-like dew points in the upper 70s to around 80 will mean that every cubic meter of air will be holding about 1.5 tablespoons of moisture. That will prevent sweat from evaporating off the human body, inhibiting one’s ability to cool oneself and exacerbating heat stress. Heat indexes will range from 113 degrees to 117 degrees through at least the end of the week.
Jackson, Miss., will face highs in the upper 90s to around 100 degrees, with this level of heat likely to persist into Friday. For Memphis, triple-digit highs — and heat indexes above 110 degrees — are likely Thursday, Friday and Saturday. And Nashville also may hit 100 each day in the same window, with similarly dangerous heat indexes.
The heat should finally begin to subside from Sunday as the parent heat dome flattens.
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