Life-threatening heat domes challenge forecasters amid climate change

Business Standard

10-07-2025

Record-breaking temperatures seared the eastern US last month, leading to power emergencies across the region. The cause: an enormous ridge of high pressure that settled on the region, known as a heat dome.
This phenomenon has also already struck Europe and China this summer, leading to the temporary closure of the Eiffel Tower and worries about wilting rice crops, respectively. But while heat domes are easy to identify once they strike, they remain difficult to forecast — a problematic prospect in a warming world.
'There is a world of difference between normal summer heat and record or near-record breaking extreme heat,'' said Scott Handel, lead forecaster at the US Climate Prediction Center. 'While normal summer heat can be dangerous, extreme heat can be particularly life threatening.'
Heat dome is used to describe extreme heat waves to the general public that captures their menace, said Zach Zobel, a scientist at the Woodwell Climate Research Center. They occur when a large high pressure system settles over a specific area, baking it under stagnant air and the sun's unrelenting energy. That locks in more heat and can intensify the area of high pressure, creating a self-reinforcing cycle.
Heat domes can occur at any time of year, but they're particularly dangerous during summer, with wide-ranging societal and economic impacts in the billions.
Wildfires and droughts are often the byproduct of extreme heat and have caused some of the largest climate-related disasters in the US. From 1980 to 2024, 23 wildfires caused $147.9 billion in damage and killed 537 people while 32 droughts extracting a toll of $367.6 billion and killed 4,658, according to a database of billion-dollar disasters that was updated until this year by the US Centers for Environmental Information.
Between 1979 and 2022, more than 14,000 Americans died directly from heat-related causes according to death certificates, the US Environmental Protection Agency said. In the summer of 2022, an estimated 61,672 people died from heat related causes, according to a July 2023 paper published in the journal of Nature Medicine.
A prolonged heat dome can stress crops, particularly heavily traded corn and soybeans. Electricity prices and demand soar when temperatures rise and stay elevated for prolonged periods, said Anthony Chipriano, a forecaster at Vaisala. The dead, hot air under these massive systems can limit the tonnage carried by airliners, kink railroad tracks and crimp the output of wind turbines.
For these reasons, meteorologists are opening their toolboxes to try and figure out where and when heat domes will strike.
'I don't have the same ability to predict heat domes like cold air outbreaks, but there are some trends,'' said Judah Cohen, director of seasonal forecasting at Atmospheric and Environmental Research Inc.
Meteorologists know, for example, the jet stream — a river of fast-flowing air girdling the globe — naturally migrates northward in summer and they can measure how fast it moves.
That metric is known as the Global Atmospheric Angular Momentum, and it's among the best predictors for heat domes, said Matt Rogers, president of the Commodity Weather Group. When the value is low, as it is two weeks ago, 'it can be a leading indicator of widespread, middle latitude heat ridges,'' he said.
The latest indication from GLAAM is the return of relatively cooler weather, Rogers said. July is tracking warmer than the 30-year average but cooler than the mean of the last 10 years and the least hot since 2021, he said.
Some weather phenomenon like the polar vortex can be spotted several weeks in advance while others like El Nino can be predicted months ahead of time. But heat domes have a much shorter lead time.
The US National Weather Service studies probable outcomes of emerging weather patterns, said Handel of Climate Prediction Center, which is what allowed the agency to start issuing heat warnings ahead of the dome that gripped the East Coast even as the region experienced relatively cool weather.
The service issued a moderate risk of extreme heat on June 13, when the high temperature in New York's Central Park was still just 78F. Ten days later, the temperature reached 96F, and it hit 99F the day after, both daily records.
Federal forecasters also rely on statistical analysis of past patterns compared to what computer models are projecting as well as measures like soil moisture since drier land means higher temperatures to put their heat forecast together.
Climate change has warmed the planet, particularly the high latitudes. That influences heat domes in two ways. The first is their northward migration. That phenomenon played out in 2023 as a large ridge of high pressure parked across western-to-central Canada and kicked off a record wildfire season.
The second is changes to the jet stream. The temperature gradient between the poles and the tropics helps keep the jet stream taut, allowing it to push weather patterns along after a few days, Zobel said. But as the Arctic warms faster than the rest of the planet, that gradient weakens and is akin to loosening the grip on a rope. The resulting slack can cause the jet stream to kink, bend and buckle. The river of air can also sometimes split, creating a 'kind of a no-man's land' that holds heat domes in place, Cohen said.
Still, Arctic warming's exact impact on the jet stream is an area of active research, Simpson said. Some papers haven't been able to show the impacts that adherents of the weakening theory suggest, and others have come up with opposite results.
What is clear is that temperatures are rising everywhere, said Karen McKinnon, an associate professor at the Institute of the Environment and Sustainability at the University of California Los Angeles, and it doesn't take that much of an increase on the hottest days to 'make summers feel substantially more extreme.'
With more heat trapped in the system and weather patterns that can lock it in place over specific locations, that makes the need for more accurate forecasts with longer lead times all the more important.
'The weather event that kills more than anybody else on the planet is heat and that is certainly true in the United States,' Zobel said. 'It is silently a big human health impact.'