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What’s a Heat Dome? Are We In for More of Them?

People rest at the Oregon Convention Center cooling station in Portland on June 28.

People rest at the Oregon Convention Center cooling station in Portland on June 28.

Photographer: Karthryn Elsesser/AFP/Getty Images
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A rare heat wave has shattered records across the U.S. Pacific Northwest and Western Canada. In a region of the world generally known for cool rain and cloudy skies, the high temperatures have buckled highways and triggered rolling blackouts. The swelter is caused by a heat dome, a weather phenomenon that can trap an entire region under searing skies for days.

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. Heat domes can actually force the jet stream, bands of strong wind that generally blow from west to east, to flow around it. In the case of the heat dome in the U.S. Northwest, that means the jet stream will flow north, causing it to slow down.