With Lessons Learned, Power Markets Enter Winter with Confidence

Until recently, most government and private forecasters have said they did not expect a repeat of last winter's prolonged periods of extreme cold that affected the East.

But that consensus was upended 10 days ago, when Andover, Mass.-based WSI issued a new forecast warning that many indicators "suggest to us that colder weather is on tap for the back half of winter, as we expect a collapse of the stratospheric polar vortex that would allow for Arctic air to make many more guest appearances in mid-latitudes again during January and February."

"This would be much different than last winter -- the stratospheric vortex did not break down last winter.  Our cold winter last year was forced by processes near the surface rather than in the stratosphere," said Todd Crawford, WSI's chief meteorologist, in an interview.

A breakdown in the stratospheric vortex occurs in half of most winters on average, Crawford said. When it occurs, warm air descends from the stratosphere to the surface at the North Pole.  "This warming of the North Pole effectively results in an evacuation of all of the Arctic air southward into midlatitudes, increasing the odds of colder temperatures in the U.S., Europe and Asia," Crawford said.  "It doesn't guarantee colder weather, but it certainly sharply increases the odds."

This year, it likely will not occur until January. "We're going to see spells of much warmer weather throughout a lot of December, especially in the Northeast," Crawford said.

This year's phenomenon would be "more eastern-based cold instead of central-based cold," such as that which happened in Illinois, Wisconsin and Minnesota in early 2014, he said.  "This winter, we expect the coldest temperatures to be along the Eastern Seaboard."

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