We’re About to See a Rare and Record-Setting May Heat Wave

We’re About to See a Rare and Record-Setting May Heat Wave

A potentially record-setting heat wave is headed for the Pacific Northwest and western Canada, a sign of the shift to hotter—and earlier—summers

A man jumps from the South Lake Union Park Bridge to the icy water below during a sweltering heat wave in Seattle in June 2021. Credit: James Anderson/Alamy Stock Photo

It may still be spring, but baking summer heat is about to hit the famously comfortable Pacific Northwest and western Canada. Starting this weekend, the heat wave will send temperatures soaring 20 to 25 degrees Fahrenheit above average in some spots and potentially break records.

This event won’t reach the heights of the punishing heat dome that obliterated records in the region in June 2021 and contributed to hundreds of deaths. But it still raises public health concerns in an area that is known for its cool, gentle summers—and whose people are not acclimatized to serious heat this early in the season, if ever. There are also concerns that the hot, dry conditions could fuel the wildfires already raging in western Canada’s province of Alberta, causing air quality problems and sending smoke all the way to the U.S. East Coast.

The new heat wave is also yet another reminder that summers are getting progressively hotter and arriving earlier as humans continue to release planet-warming emissions into the atmosphere.

In the Pacific Northwest, the latest unseasonably high temperatures are coming courtesy of a high-pressure system, or ridge, that is moving through the atmosphere over the region and pulling in warm air from the south. The cloudless skies that come with high-pressure systems also let the sun beat down and warm the surface. “Each day it’s there, it strengthens,” which will cause temperatures to rise over the weekend to an expected peak on Sunday or Monday, says Kayla Mazurkiewicz, a meteorologist at the National Weather Service’s (NWS’s) Seattle office.

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The current meteorologic setup is very similar to the one that caused the infamous 2021 heat dome over this area, says Daniel Swain, a climate scientist at the University of California, Los Angeles, and the National Center for Atmospheric Research. Though the current ridge is occurring earlier and is centered farther north, it is still “a huge blob of essentially unprecedented atmospheric high pressure and temperatures for this time of year,” Swain says. This heat wave will have lower absolute temperatures in part because the event will happen a month earlier than the 2021 heat dome. The background temperatures are still somewhat cooler.

Still, temperatures could get up to the low- to mid-90s F in some areas under the ridge. It’s possible daily records could be broken in some spots, says Miles Higa, a meteorologist at the NWS’s office in Portland, Ore. And it’s not just the daytime highs that are a concern but also unusually warm nighttime lows—particularly in a region where air-conditioning is not as prevalent as in other places and where nighttime breezes are routinely relied on as a key means of cooling down homes and bodies. “That adds to the overall heat stress for people,” Higa says.

The 2021 event shattered all-time highs in several places: it reached 116 degrees F in Portland, 107 degrees F in Seattle and 121 degrees F in Lytton, British Columbia—a village that was subsequently largely destroyed by a heat-fueled wildfire. Analyses that looked for the fingerprints of climate change in extreme weather events found that such a severe heat wave in the region should be rare even with climate change. Among them, one study calculated that it was a one-in-10,000 year event. “That was just very, very extreme,” Higa says.

But even though the coming heat wave won’t be that intense, officials in Portland and Seattle have warned residents to be careful during any outdoor physical exertion—the usual weekend yard work or Saturday run can pose a threat when your body isn’t used to higher temperatures. Such heat is particularly dangerous for young children, the elderly, those who already have certain health problems such as asthma and cardiovascular disease and people in low-income communities. Officials have also warned people to be careful if they go for a cooling dip in inviting-looking local rivers, because the snowmelt season is still going on, and water temperatures are very cold—incongruously posing a risk of hypothermia.

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The Cascade Range had a substantial snowpack coming out of this winter. And the Pacific Northwest, like much of the western U.S., normally relies on the slow melt of that snow for a steady source of water as spring and summer gradually heat it up. But heat waves like this one can cause the snow to melt rapidly—too fast for the ground and artificial reservoirs to soak it all up. “This heat wave is going to do in the snowpack for many areas,” particularly at lower elevations, says Larry O’Neill, a climate scientist at Oregon State University and director of Oregon Climate Services. If snows continue to rapidly melt through the summer, that could leave streams in tough shape by season’s end, O’Neill says.

In Alberta, officials are watching the wildfires that have already been blazing in the northern parts of the province amid concerns that the hot, dry weather could exacerbate them. The fires have led to poor air quality in vast areas downwind and have even colored sunsets as far away as Washington, D.C. The health effects of heat are also a growing concern in Alberta, which has historically been much more synonymous with cold, snowy winters. “We are better prepared for colder weather,” says Shelby Yamamoto, an environmental epidemiologist at the University of Alberta, but heat “is increasing as a priority.”

Though no specific study of the role of climate change in the upcoming event yet exists, it is clear that summers everywhere are heating up. Any heat wave that happens now can be expected to be warmer than it would have been in decades past. Summer is also increasingly expanding its reach while winter’s realm is simultaneously shrinking: A 2021 study found that over the entire Northern Hemisphere, meteorologic summer increased from 78 days in 1952 to 95 days by 2011. And the Pacific Northwest has seen clear trends in hotter summers. The average summer temperature in both Portland and Seattle is now about three degrees F warmer than it was in 1970, according to an analysis of climate records by Climate Central, a nonprofit climate research organization. The region is experiencing more days above 90 degrees—which is the threshold for extreme heat in that mild climate—and will expect to see those days coming steadily earlier in the season, O’Neill says. “What would once be considered a nice warm spring day can now rise above that 90-degree mark,” he adds.

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    Andrea Thompsonan associate editor at Scientific Americancovers sustainability.Follow Andrea Thompson on TwitterCredit: Nick Higgins

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