What Exactly Is a “Heat Dome,” The Weather Phenomenon Cooking the Northwest?

This isn’t a simple heatwave, and climate change is making it worse

The sun rises over the mountains. In the Pacific Northwest, a heat dome has led to record-breaking temperatures.
The Pacific Northwest has seen record-breaking temperatures thanks to a weather phenomenon called a "heat dome."
Kseniia Zaitseva/Unsplash

On Monday in Seattle, the city reached a high of 108 degrees. At Portland International Airport, it got up to 115. And in Salem, the capital of Oregon, the town peaked at 117 degrees. All of these, as noted by The New York Times, are record highs in Pacific Northwest areas known for their moderate temperatures. 

While some have been calling this a heatwave, the scorching temps are more accurately the product of something called a “heat dome.” 

What is a “heat dome,” exactly? The Washington Post described it like so: “When the summer sun warms air above the ground or ocean, that air can then rush up into the atmosphere to form a mountain — or dome — of slow-moving hot air under higher pressure that blocks new weather systems from moving in. Basically, it’s a mass of warm air that’s stuck over a certain area.”

Instead of a heatwave moving across the country, picking up steam and dissipating, these heat domes sit on top of an area like a grill hood, keeping the hot temperatures in place and keeping out weather systems that could cool things down. Now, these domes are not new phenomena, but as Bloomberg reported, climate change is making them much more intense. 

According to Bloomberg, there are two main factors to consider when assessing the impact of climate change on this particular heat dome: first, human-caused greenhouse gas emissions are leading to higher average and extreme temperatures around the world; and second, there are certain atmospheric circulation patterns that can lock weather systems in place, and those patterns may increase as temperatures rise, according to research.

In other words, don’t expect these record-breaking temperatures to stay records for long.

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