Extreme-heat warnings are in effect for about 143 million Americans this week, due to a heat dome that is hovering over the Midwest, South and Southwest. This dangerous heat is already smashing temperature records dating back to at least 1950, according to weather trackers.
The “searing August heat wave,” as the National Weather Service (NWS) put it, is expected to persist in at least 22 states until the end of the week, and “numerous” temperature and heat-index records are likely to be set.
The heat index calculates a “real feel” temperature that includes the effects of humidity. Dallas-Fort Worth, for instance, hit 106 degrees Fahrenheit Tuesday when just measuring air temperature, not humidity, as the metro area entered a 40th straight day of temps above 100 degrees F. Down the road, Austin had endured 44 straight days of temperatures above 100 degrees F, crushing the old record of 27 days.
According to AccuWeather meteorologist Jake Sojda, “the heat dome over the central U.S. is unusually strong, even by mid-summer standards. A unique combination of intense heat and sunshine, light winds underneath the center of the heat dome, and evapotranspiration — a process by which plants give off water, which is sometimes referred to as ‘corn sweat’ — from corn and other crops now maturing in late summer is also leading to very high humidity combined with heat.”
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Texas wasn’t the only hot spot. The heat index neared 127 degrees F in parts of Oklahoma and as much as 134 degrees F in Lawrence, Kan.
Very southern Texas found some temperature relief, although had to brace for dangerous winds, when Tropical Storm Harold came ashore early Tuesday, the first hurricane of the 2023 Atlantic season to make landfall.
The August temperature streaks follow the hottest July on record. July accounted for record electricity usage in Texas, which operates its own electrical grid. High heat forecasts can be built into power-usage plans and Texas does typically have hot summers. But the string of consecutive days of extreme temperatures put enormous stress on utilities and power lines, at the same time that air conditioning becomes critical to health and safety.
“Any power outages due to high strain on the energy grid can limit the availability of air conditioning and a way to escape the heat for some, further adding to the danger from the extreme heat,” said Sojda.
Heat domes defined
A heat dome occurs when the atmosphere traps hot ocean air like a lid over a certain area. It is associated with a blocking jetstream.
Climate change, which is warming our oceans along with the regular patterns of El Nino and La Nina, is seen as a contributing factor to extreme heat. Scientists always emphasize the difference between short-term weather and long-term climate change and they stress that the influence of climate change on blocking jetstream patterns is an active area of research.
But it is the increased frequency and the worrisome potency of weather extremes that scientists link to human-generated global warming from the burning of fossil fuels like coal, oil and gas, the result of carbon-dioxide and other emissions. Increasingly, the number of new record high temperatures is outpacing the number of record lows.
A team of scientists funded by the National Oceanic and Atmospheric Administration (NOAA) MAPP Program investigated what triggers heat domes and found the main cause was a strong change in ocean temperatures from west to east in the tropical Pacific Ocean during the preceding winter.
Read: Why the rush to curb climate change? Damaging carbon dioxide is 50% higher than at the dawn of the industrial era
As NOAA scientists explain, imagine a swimming pool when the heater is turned on. Temperatures rise quickly in the areas surrounding the heater jets, while the rest of the pool takes longer to warm up. If one thinks of the Pacific as a very large pool, the western Pacific’s temperatures have risen over the past few decades as compared to the eastern Pacific, creating a strong temperature gradient, or pressure differences that drive wind, across the entire ocean in winter.
In a process known as convection, the gradient causes more warm air, heated by the ocean surface, to rise over the western Pacific, and decreases convection over the central and eastern Pacific. As prevailing winds move the hot air east, the northern shifts of the jet stream trap the air and move it toward land, where it sinks, resulting in heat waves.
Drought conditions can have their own effect. When drought conditions are in place, dry soil heats more easily than moist soil, contributing to the higher temperatures near the ground. And as the climate warms, soils dry out more quickly and drought risks increase, reinforcing the cycle.
(Read more on the relationship between carbon dioxide and long-run temperatures and click here for city-by-city temperature trends.)
The strength of this particular heat dome appears to be topping one that occurred during August 1936, which was in the midst of the “Dust Bowl” that contributed to the Great Depression.
And when might relief be expected?
“During the second half of the week, the northern periphery of the heat dome will gradually be eroded as multiple waves of energy from Canada and the Pacific begin to usher cooler air back into the region,” said AccuWeather’s Sojda. “However, most of this relief will not reach portions of central Plains and southern U.S. until this weekend or early next week as the strong heat dome will only retreat farther south.”
