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Map showing much hotter than normal conditions across the Pacific Northwest and British Columbia on June 27. Credit: Weathermodels.com

The extraordinary heat wave that's stifling the Pacific Northwest reached its peak in many areas on Monday. Seattle smashed its all-time high-temperature record, set just the day before, by 4°F.

Why it matters: After two days of oppressive heat and little relief at night, the extreme weather event, boosted by global warming, is moving into a more dangerous phase.

  • Heat illness tends to spike the longer heat waves last, and extreme heat is the No. 1 weather-related killer each year in the U.S.

Driving the news: A highly unusual weather pattern that statistically has less than a 1-in-several-thousand-year chance of occurring is in place over the Pacific Northwest, with a record-strong high-pressure area aloft — colloquially known as a "heat dome" — sitting over Washington state and British Columbia.

  • This heat dome is yielding temperatures 25–50°F above average across multiple states and British Columbia.
  • This heat, combined with a worsening drought, is raising the risk of wildfires across multiple Western states, with some large blazes erupting in California Sunday and Monday.
  • It is also causing power demand to spike at a time when hydropower resources are lower than usual.
  • The heat was so severe Monday that pavement buckled across the Seattle and Portland metro areas.

By the numbers: All of Oregon, Washington and Idaho, plus portions of California, Montana and Nevada, are under excessive heat watches and warnings.

  • Portland, Oregon, set an all-time high temperature of 112°F on Sunday, and eclipsed that on Monday, with a high of 115°F.
  • In Seattle, the temperature reached 104°F on Sunday, which broke the existing all-time record. It exceeded this on Monday, reaching 108°F.
  • Before this weekend, Seattle had never had back-to-back 100-degree days, and only saw three such days on record. But now, the century mark was exceeded three days in a row.
  • A preliminary state record of 118°F was tied in Dallesport, Washington.
  • Canada is also seeing extreme heat, with the country's June high-temperature record tied on Saturday and smashed on Sunday at Lytton in British Columbia by nearly 3°F, with a high of 116°F. This was broken again Monday, with the same location recording 117.5°F.

Of note: To put this into perspective, this means that a location in British Columbia, not known as an extremely hot province in June, equaled Las Vegas' all-time hottest temperature.

  • Mountain areas in the Northwest have been extremely warm with freezing levels located above the peak of Mount Rainier at times. This is resulting in rapidly melting snow and ice, from the peaks of Oregon to the mountains of British Columbia.

How it works: There are three main reasons the Pacific Northwest is so hot. The first is tied to the heat dome itself, which causes air to sink, or compress, warming as it does so and keeping skies clear. The second has to do with the location of the heat dome.

  • The feature is parked to the north-northeast of the region, at the same time as an upper-level low-pressure area lurks offshore.
  • Due to the clockwise flow of air around the high pressure, easterly winds are blowing from high-to-low elevation areas, adding even more compressional heating.

The third fact is climate change. Studies have shown that severe heat events such as this one are now on average about 3–5°F hotter than they would be without the many decades of emissions of greenhouse gases from fossil fuel burning, deforestation and other human activities.

  • However, this understates climate change's influence, researchers told Axios, as warming is also thought to be altering weather patterns in a way that makes strong heat domes more common and prolonged.
  • Climate scientists warn that this event demonstrates how climate change plus natural weather variability are pushing society beyond our ability to cope.

What they're saying: "We have made trillions of small adaptations to optimize our society for the historical range of temperature, precipitation, etc., that we have experienced," Andrew Dessler, a climate researcher at Texas A&M University, told Axios via email.

  • "As the climate changes, that range is no longer the relevant one, and the mismatch between what we are adapted for and what we actually experience can generate huge negative impacts that seem to suddenly appear out of nowhere — even though we've been predicting them for literally decades," he said.
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Go deeper

Dangerous Pacific Northwest heat wave shifts inland

NASA computer model image showing the unusual heat in the Pacific Northwest and British Columbia. (NASA Earth Obseravtory)

After reaching an unprecedented peak, the ferocious heat wave in the Pacific Northwest is retreating inland on Tuesday, sparing some of the biggest cities, including Seattle, from another day of record-breaking heat.

Why it matters: The worst heat wave on record in the Pacific Northwest has had a wide range of impacts, from damaging public transit infrastructure — rails failed and roads buckled — to public health issues. This event is not over, given the continued record high temperatures in areas further away from the coast.

Northwest "heat dome" signals global warming's march

Residents gather in a public cooling shelter set up at the Oregon Convention Center during a heat wave in Portland on June 26, 2021. (Maranie Staab/Bloomberg via Getty Images)

The dangerous heat wave enveloping the Pacific Northwest is shattering weather records by such large margins that it is making even climate scientists uneasy.

Why it matters: Infrastructure, including heating and cooling, is built according to expectations of a "normal" climate. Human-caused climate change is quickly redefining that normal, while dramatically raising the likelihood of events that simply have no precedent.

Jun 28, 2021 - Podcasts

The Pacific Northwest's extraordinary heat wave

The Pacific Northwest is experiencing record-high temperatures due to a “heat dome” that should be a once every-few-thousand-year event — but which could occur more often and with more severity due to climate change.

Axios Re:Cap goes deeper with Axios climate reporter Andrew Freedman, to better understand this weather event's science, the dangers posed to human health and infrastructure and how the definition of "normal climate" is changing.