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We’re having a heat wave

Last updated Jul. 27, 10:03 AM EDT

Only three days of 90-degree heat are needed for a heat wave to be declared. As of Tuesday, Boston has had six in a row. Read more coverage.

A Camp Vibrant participant cools off in the Christian Science Center fountain. Jessica Rinaldi / Globe Staff
A Camp Vibrant participant cools off in the Christian Science Center fountain.

Boston’s current heat wave

Temperatures across the U.S.

SOURCE: National Weather Service SOURCE: National Weather Service
SOURCE: National Weather Service

A very hot and humid air mass will persist over much of the east over the next couple of days. This slow-moving high pressure zone has been referred to as a “heat dome.” Essentially the high pressure in the middle and upper layers of the atmosphere act as a kind of cap that causes heat to build up at the earth’s surface.

At the Franklin Park Zoo, Katherine Rodriguez keeps cool using her umbrella and a misting fan set up by the zoo. Suzanne Kreiter/Globe Staff
At the Franklin Park Zoo, Katherine Rodriguez keeps cool using her umbrella and a misting fan set up by the zoo.

How hot has it been?

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