Since late June, bouts of extreme heat have scorched both the United States and Europe. To blame are large, stagnant zones of high pressure known as heat domes.
They are known to produce record-breaking high temperatures, and they also can fuel violent thunderstorms, stoke dangerous wildfires, and exacerbate drought.
These heat domes baked the western U.S. and Europe in June and early July, the eastern U.S. in mid-July and then Europe again last week. Their sweltering conditions helped heat the planet to its warmest June and what may become its warmest July on record.
They form several miles high in the atmosphere and their air sinks down toward the ground, heating up due to compression. Sometimes they produce a dry heat, but when they are located near water, they can circulate oppressive humidity as well.
Heat domes often form what are known as blocking patterns in the atmosphere, which halt the west-to-east movement of weather, and their stifling conditions can last for days.
We typically see three different kind of blocks resulting from heat domes in the U.S. and Europe: omega blocks, rex blocks, or sprawling high pressure blocks which can create what’s known as a ring of fire weather pattern. Regardless of their shape, the blocks often provide three to five days of relentless heat until the pattern weakens or is pushed out.
Sometimes large blocking high pressure systems that form over the southern U.S. help form what’s known as a ring of fire weather pattern.
Such a pattern developed over the central U.S. in mid-July when a heat dome formed in the South and expanded north and east. Sweltering heat overtook much of the East Coast, fueled by warm humid air flowing north from the Gulf of Mexico. It produced heat indices exceeding 110 degrees in some areas and suffocating nighttime temperatures that did not drop below 80 degrees. Boston posted its hottest weekend on record.
This expansive heat dome gave rise to the ring of fire pattern, named for the corridor of thunderstorms, some severe, arched along its northern periphery.
As the climate has warmed in recent decades, such heat domes have become more intense. An analysis from meteorologist Ryan Maue showed the strength of summer high pressure zones in the western U.S. increasing over time. Similarly, a study conducted by researchers in State College showed increases in the frequency of such warm pockets over much of the Northern Hemisphere.
As the climate continues to warm, expect to hear more and more about these hot high pressure zones and their punishing impacts.