An oppressive heat wave has engulfed western US that has killed at least seven people, according to authorities. The city of Las Vegas surpassed recorded fifth consecutive day of temperatures at 46.1 degree Celsius.
Even by desert standards, the prolonged baking that Nevada’s largest city is experiencing is nearly unprecedented, with forecasters calling it “the most extreme heat wave” since the National Weather Service began keeping records in Las Vegas in 1937, according to the Associated Press.
Las Vegas area has been under an excessive heat warning on three separate occasions this summer, totaling about 12 days of dangerous heat with little relief even after the sun goes down, meteorologist Morgan Stessman.
In California, at least a dozen cities broke all-time high-temperature records. Between July 5 and July 6, the mercury soared 48.33 degree Celsius and 47.22 degree Celsius in Redding, a city in Northern California, and Ukiah, north of San Francisco, respectively. Palm Springs, in Southern California, touched a record-breaking high of 51.11 degree Celsius.
The scorching temperatures are being driven by a heat dome.
What is a Heat Dome?
A heat dome is created when warm air becomes trapped beneath a stagnant patch of high-pressure air in the atmosphere, according to the Royal Meteorological Society. Heat domes can block weather from passing through, causing extreme heat conditions.
The phenomenon is associated with unusually warm periods in India, Bangladesh, China and some other Asian countries.
The high-pressure system allows more sunlight to reach the earth, which results in more warming and drying of soil. This leads to less evaporation and reduces the likelihood of the formation of rain clouds. The longer the heat dome stays in one place, the warmer conditions can get with every passing day. While heat domes cause heatwaves, they can occur without heat domes as well.
A heat dome usually lasts from a few days to a few weeks. But it’s hard to predict how long a heat dome will persist, because they are linked to the behaviour of the jet stream.
What is a Jet Stream?
A jet stream is a fast, narrow current of air flowing from west to east that encircles the globe. It has a wave-like pattern that keeps moving from north to south and then north again. When these waves get bigger and elongated, they move slowly and sometimes can become stationary. This is when a high-pressure system gets stuck in place, and leads to the occurrence of a heat dome.
According to National Geographic, jet stream speeds usually range from 129 to 225 km per hour (80 to 140 miles per hour), but they can reach more than 443 km per hour (275 miles per hour). They are faster in winter when the temperature differences between tropical, temperate, and polar air currents are greater.
There are two jet streams: a subtropical jet stream centered at about 30 degrees latitude and a polar-front jet stream whose position varies with the boundary between polar and temperate air. A reverse jet stream blows toward the west in tropical high altitudes during the Northern Hemisphere’s summer. It is associated with the heating of the Asian continent and may help bring summer monsoons to the Indian Ocean.
How Many People Are Affected in the US?
Some 20 million Americans, from California to Texas, were living under a federal excessive heat advisory as of Wednesday, with forecasters issuing alarms about the heat dome in the Western US. Another 11 million people were under heat advisories.
How Climate Change Affects Heat Domes?
Climate change has led to warmer background temperatures, exacerbating the high-pressure system. Regions that have become drier due to the same, can also create conditions that are beneficial to the formation of heat domes, according to Down to Earth.
According to a 2021 study carried out by an international team of 27 climate researchers, who were part of the World Weather Attribution, searing temperatures recorded during the heat dome in Canada, which occurred in June that year, “would have been virtually impossible without the influence of human-caused climate change”.
Another study, published in the journal Nature 2023, showed that the intensity of heat domes is outpacing the rate of global warming — which means that climate change is fuelling their intensity.
How Can People Stay Safe in a Heat Dome?
• Never leave people or pets in a closed car on a warm day.
• If air conditioning is not available in your home go to a cooling centre.
• Take cool showers or baths, wear loose, lightweight, light-colored clothing.
• Use your oven less to help reduce the temperature in your home.
• If you’re outside, find shade. Wear a hat wide enough to protect your face.
• Drink plenty of fluids to stay hydrated.
• Avoid high-energy activities or work outdoors, during midday heat, if possible.
• Watch for heat cramps, heat exhaustion and heat stroke.
• Consider pet safety. If they are outside, make sure they have plenty of cool water and access to comfortable shade.