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The idea is the jet stream — the upper air circulation that drives weather — is wavier in amplified global warming, said University of Wisconsin-Madison climate scientist Steve Vavrus.

And those wave changes in the upper air knock the polar vortex out of its place and toward the United States, Cohen said.

“The upper air observing program remains a key contributor to our analyses, model data assimilation, and for our forecasters’ situational awareness,” she said.

Charles King teaches at Georgetown University and is the author of “Gods of the Upper Air” and other books.

But to me, they are creatures of the upper air, and of their nature unintelligible, which makes them more akin to angels.