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Splitting the polar vortex: Is the globe spinning the wrong way?

By Judah Cohen March 9, 2018

Splitting the polar vortexSpain, Italy, Ireland, England, and several other countries spanning Europe that can usually expect more temperate winter weather were hit earlier this month by Arctic winds, bitter cold, and crippling snowstorms that wreaked havoc and took lives.

Across the Atlantic, the United States and Canada also suffered through a parade of brutal storms. When the storms reach the East Coast, they are known as Nor’easters. This month, the first dumped 40 inches of snow on upstate New York and brought to Boston 93 mile-per-hour hurricane-force winds along with one of the three highest tides on record. The second Nor’easter brought two feet of snow to the New York City metro area and cut power to a million customers.

Warmer in the North Pole

It was relatively balmy in the North Pole by contrast. In that frozen terrain where subfreezing temperatures are to be expected, the data shows that temperatures soared 45 degrees above normal this month to 35 degrees Fahrenheit. And that was in the middle of winter with no sun.

What’s going on?

Blame it on the splitting of the polar vortex, a wall of wind that swirls around the Arctic and prevents warm air rushing in and cold air rushing out. This month, like a refrigerator door left open for too long, warm, high-pressure winds rushed into the Arctic, and low-pressure cold air rushed out, travelling in an abnormal east-to-west pattern that affected much of northern Eurasia and North America. (See animation below, which illustrates this phenomenon as it unfolded in January and February 2018.)

In short, the splitting into two pieces of the polar vortex sucked frigid air out of Siberia and pushed it counter to the normal Jetstream flow, across Europe and beyond. (This period also marked one of the rare times it took you less time to fly from Europe to North America than from North America to Europe.)

For some time, scientists at Verisk’s Atmospheric and Environmental Research (AER) business have been tracking the polar vortex using our proprietary statistical model to observe weather trends going back decades. Using observational data, we predicted a month ago with some certainty the February/March 2018 weather extremes we’ve recently experienced – a rare feat in weather forecasting.

AER illustration of the Polar Vortex split

Figure Caption: At the beginning of the animation, the polar vortex lies near the North Pole and it confines all the cold air (blue shading) around the Arctic. However, as the animation advances in time, warm air (orange and brown shading) emerges out of Siberia and the North Atlantic and splits the polar vortex into two pieces. One center of the polar vortex heads to Canada while the sister vortex heads to Europe. The contours show the initial flow occurs from west to east, and then the flow becomes more north and south across North America as the cold air spills out from the Arctic into the Western U.S. Across Europe, the counter-clockwise flow around the sister vortex ushers cold air from Siberia west across Europe and is known as the “Beast from the East."

Historically speaking, what correlations have we been seeing? The polar vortex split previously in 2010, 2013, and 2015. In 2010, Washington, D.C., experienced unprecedented, back-to-back snowstorms and New York City registered its snowiest month in history. In 2013, the splitting of the polar vortex ushered in Winter Storm Nemo, a blizzard that dumped 30-to-40 inches of snow from Long Island through Southern and Eastern New England. And in 2015, the split of the vortex preceded the snow blitz in the U.S. Northeast, which buried the Northeast under mountains of snow, crippling transportation and resulting in a record number of roof collapses.

To be sure, we can expect continued extreme weather patterns because the vortex remains weak, slowing the movement of the Jetstream and giving these types of storms more time to gather strength.

Implications for insurers

What are the implications for insurers? To put it into perspective, my former colleague Paul Walsh, now a weather and business expert at The Weather Channel, estimated a $1 billion impact from Winter Storm Quinn alone, just from an "insurance perspective and a damage loss perspective.” And, he told the newsmagazine U.S. News and World Report, "It's going to include insured losses, which are probably over $500 million."

Dr. Judah Cohen is director of seasonal forecasting at AER.