Jan 3, 2018

Here's the science behind why it's been so cold lately

United States
by
Omaha World-Herald via AP
 A layer of ice is broken into pieces floating along the Hudson River at the Palisades Interstate Park on Tuesday in Fort Lee, New Jersey. Photo: AP
A layer of ice is broken into pieces floating along the Hudson River at the Palisades Interstate Park on Tuesday in Fort Lee, New Jersey. Photo: AP

Anchorage, Alaska, was warmer Tuesday than Jacksonville, Florida. The weather in the U.S. is that upside down.

That's because the Arctic's deeply frigid weather escaped its regular atmospheric jail that traps the worst cold. It then meandered south to the central and eastern United States.

And this has been happening more often in recent times, scientists say.

WHY IS IT SO COLD?

Super cold air is normally locked up in the Arctic in the polar vortex , which is a gigantic circular weather pattern around the North Pole. A strong polar vortex keeps that cold air hemmed in.

"Then when it weakens, it causes like a dam to burst," and the cold air heads south, said Judah Cohen, a winter storm expert for Atmospheric Environmental Research, a commercial firm outside Boston.

"This is not record-breaking for Canada or Alaska or northern Siberia, it's just misplaced," said Cohen, who had forecast a colder than normal winter for much of the U.S.

IS THIS UNUSUAL?

Yes, but more for how long — about 10 days — the cold has lasted, than how cold it has been. On Tuesday, Boston tied its seven-day record for the most consecutive days at or below 20 degrees that was set exactly 100 years ago.

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WHAT MAKES THE POLAR VORTEX MOVE?

This is an area of hot debate and research among scientists and probably is a mix of human-caused climate change and natural variability, said Furtado. Climate change hasn't made the polar vortex more extreme, but it probably is making it move more, which makes the weather seem more extreme, he said.

A recent study by Potsdam Institute climate scientist Marlene Kretschmer found the polar vortex has weakened and meandered more often since 1990, but that study focused more on Europe. Ongoing research shows that there seems to be a similar connection for more frequent Arctic cold snaps like what the U.S. is now experiencing, Kretschmer said.