For the last couple of weeks, parts of the southern US and Mexico have been enduring severe heat, with temperatures soaring to record highs in several cities in Texas. For example, Del Rio, a city on the Texas/Mexico border, has seen 8 straight days with daily record highs, all in the triple digits (in Fahrenheit). The heat index is how hot it feels to the human body when humidity is factored in as well: this reached an unofficial record of 125 degrees Fahrenheit (52 degrees Celsius) in Corpus Christi, Texas. What’s going on – and is there any relief in sight?
Heat events which are more intense, last longer and happen more frequently have been predicted by climate change experts. What’s parked over Texas and Mexico since early June is an example of a “heat dome” fueled by climate change. If you recall last spring (2022), another heat dome parked itself over the Pacific Northwest and Canada, which unfortunately helped fuel wildfires.
So what is a heat dome? First it’s important to know that because the Earth’s surface is unevenly heated, this causes areas of high and low pressure to develop. A low-pressure system features rising air which eventually cools, condenses, and forms clouds and precipitation. A high-pressure system features sinking air which compresses and becomes warmer, bringing clear skies and lots of sunshine. When a high-pressure system gets stuck over an area, it’s called a “heat dome.” To completely dissipate it requires a big push from either the jet stream – the fast-moving current of air that guides weather systems around the Northern Hemisphere – or another relatively strong system higher up in the atmosphere.
Believe it or not, there’s a connection to the Arctic here: due to the rapid warming of the far North, this is altering the jet stream in a way that makes weather patterns “stick.” The temperature difference between the North Pole and equator is less now, meaning the jet stream winds are slowing down, causing the jet stream to occasionally dip towards the south. Think of what happens when a spinning top starts to slow down – it wobbles. These jet stream “wobbles” or dips can cause storms to stall and intensify rather than move away as they normally would do. At the mid-latitudes, this results in more extreme droughts, floods, cold spells (recall, Texas endured an Arctic cold snap in February 2021) and heat waves, like what is currently going on.
The latest models forecast the dissipation of the current dome after July 4th. This week, the dome is slowly shifting to the north and east, meaning Louisiana, Arkansas, Mississippi, Alabama, Missouri, Tennessee, Georgia and Florida are next when it comes to reaching the triple digits. If you’re in these regions, it’s important to limit strenuous outdoor activity. If you have to work outdoors, take plenty of breaks (ideally indoors with A/C or at least in the shade) and drink plenty of water and electrolytes.