Lined up like a parade, the heat domes are also part of a traffic jam of weather systems that instigated the flood disaster in Europe last week.
Heat domes like this are normal at this time of year, the hottest point of summer, but it’s unusual to have this many this intense. Every one of these heat domes is generating exceptional weather.
A trip around the heated hemisphere
Starting in the western United States, temperatures in Montana climbed more than 20 degrees above normal on Monday. Glasgow, Mont., spiked to 110 degrees, matching its third-highest temperature on record since 1893. Billings hit 107 degrees, tying its second-highest temperature recorded since 1934. The heat is worsening exceptional drought conditions in both the western United States and Canada, creating tinderbox conditions for wildfires that are spreading smoke all over North America.
Across the Atlantic, the heat dome lodged over the British Isles brought Northern Ireland its hottest day on record Sunday, which was then broken four days later.
The heat dome has hardly budged, prompting the Met Office, Britain’s meteorological agency, to issue its “first ever” extreme heat warning Monday. The warning, in effect through Thursday, calls for prolonged unusually high temperatures over “a large part of Wales, all of southwest England and parts of southern and central England,” the agency wrote. Temperatures may reach the low 90s in this zone.
“As we experience the first hot weather episode of the year, it’s important for everyone to remember to adapt their behaviours,” Owen Landeg, Public Health England’s scientific and technical lead, wrote in a news release.
Farther east, the heat dome parked over southeastern Europe and Western Asia has also produced exceptionally high temperatures. On Tuesday, the thermometer in the Turkish city of Cizre, near the border with Syria, surged to 120.4 degrees, the country’s highest temperature ever observed.
Etienne Kapikian, a meteorologist with Meteo France, the country’s meteorological agency, tweeted he expects this heat wave to produce additional record-challenging temperatures into Wednesday in adjacent areas, including in Syria, Armenia, Georgia, Iraq, Iran, Azerbaijan and Russia.
Farther to the east and north, record heat has also invaded northern Japan, where all-time highs were set on Sunday and Monday. In Hokkaido, Japan’s northernmost island known for its ski resorts and abundant winter snowfall, “the heat was so intense that the train rails were distorted,” tweeted Sayaka Mori, a meteorologist based in Tokyo.
The exceptional heat also bled into eastern Russia and Siberia, where a siege of wildfires has torched the landscape.
Finally, crossing the Pacific, much warmer-than-normal temperatures cover Alaska. The responsible heat dome is the least intense of the five affecting the Northern Hemisphere. Even so, it pushed the mercury to 81 degrees in Anchorage on Sunday, a record for July 18 and tied for the city’s 16th-warmest day ever observed, according to Alaska-based climatologist Brian Brettschneider.
The heat over the Last Frontier has helped fuel unusual thunderstorm outbreaks in recent days, including some over the Arctic Ocean sea ice north of its border.
A weather pattern fueled by climate change
Scientists have determined that climate change is increasing the intensity of heat domes and making heat waves hotter than they would have been without human influence. This explains the frequency at which temperature records are being set every summer. Already this summer, seven national high temperature records have fallen.
But the current weather pattern, in which these heat domes are not only intensified but also prolonged, may also be linked to climate change.
Climate change is expected to decrease the strength of steering currents as the high latitudes warm more quickly than the mid-latitudes, reducing the north-to-south temperature differences that drive the wind. According to a 2018 study from climate scientist Michael Mann of Pennsylvania State University, weaker high altitude winds will produce a slower jet stream with more wavy peaks and troughs, which he ascribes to a process known as “quasi-resonant amplification.”
The more wavy peaks are the breeding grounds for intensified heat domes, like we see spread around the Northern Hemisphere, while the troughs are the low-pressure zones that can set the stage for floods like we just saw in Germany and neighboring countries.
The configuration of heat domes we see at the moment looks like a “classic” example of a pattern “associated with wave resonance,” Mann wrote in an email.