Record Northwest Heat Details

How Did It Get So Hot?

As with most questions about the atmosphere, there are multiple answers. The most direct cause of the blistering heat was a high-pressure system, stronger than ever observed in the region, that sat over the region for several days, unwilling to move like a stubborn dog on a walk. The cloudless skies and sinking air associated with the high pressure helped record temperatures build.

Adding to the heat in some locations was the prevailing winds, which in the Northern Hemisphere always blow clockwise around high pressure. Due to the topography of the region — mountains and high plateaus — easterly winds bring air from high elevation to lower elevations, which causes it to compress and heat up. These winds are called downslope winds, and they are known to kick temperatures up a notch all along the West Coast.

And finally, while there has not been an attribution study yet on this heat wave, climate change likely had an influence as well. As noted in the article on the previous record temperatures, heatwaves across the contiguous United States have occurred more often and lasted longer since the 1960s. According to NOAA’s Climate Extremes Index, the percent area of the Pacific Northwest that has experienced summertime extreme temperatures has drastically increased over the last 20 years. For the first 90 years of the record, an extreme heat footprint of larger than 50% of the area happened only three times. In the past 20 years, it has happened six times.

In the future, according to the Climate Science Special report, the scientific basis for the fourth National Climate Assessment, heatwaves are projected to continue to get hotter, occur more often and last longer in the future due to the emissions of greenhouse gases.

Dangers of Heat in the North

Extreme heat this far north is particularly dangerous as these locations have a lot less experience with temperatures that high. Communities in the Southwest, for instance, have previous knowledge of temperatures over 100 degrees. Those in the Northwest and Canada simply do not. And this manifests itself through the built environment. Air conditioner use in the Southwest is virtually mandatory. Yet in Seattle, according to the New York Times, there is a culture against air conditioner use. NPR notes that Seattle ranked as the least air-conditioned city in a comparison of the top 15 metro areas in the U.S. Only 44% of homes in Seattle have primary air conditioning installed. Things are slightly better in Portland, at 78% of homes, but still far below the nationwide average.

Commenting on the event in a list-serve for weather experts, Seattle resident Dale Duran, a professor in the atmospheric science department at the University of Washington described covering his windows with foam-core insulation board to block the incoming sun. “It’s not just that we don’t have air-conditioning,” he wrote. “It’s that our built environment is optimized for what used to be our climate. In Seattle, we build modern houses in a way that would be inconceivable in a hot climate. We not only do not have air-conditioning, we like to have lots of windows, including south-facing ones. Many of those windows don’t have any window coverings. They also don’t have sun-blocking film (for most of the year we’d prefer to have that heat come in).”

A lack of resources to cool a population during extreme heat conditions can lead to dangerous health outcomes. It’s likely too early to know the full health toll from this heatwave but it serves as a reminder of dangers of the extreme heat, both today and in a warming world.”

More details and additional graphics are at this link:…

Bryce Anderson can be reached at

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