Polar Vortex Pays Return Visit to US

The eastern two-thirds of the nation has been enjoying above-freezing temperatures over the past week, but that's about to come to an icy end.

The polar vortex is coming back, and will bring frigid temperatures along with it from Minneapolis to New York, reports AccuWeather.

The temperatures soared last last week to the relatively balmy mid-60s in Washington, D.C., and Philadelphia and into the 50s in New York City and Boston, but starting Monday, the highs will drop by a good 10 to 20 degrees in the Northeast and mid-Atlantic states.

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Colder air already has hit the Midwest, reports AccuWeather, and Sunday is expected to be the warmest day this week. Waves of cold are are coming from the Arctic into the Midwest, northern Rockies and Northeast as the polar vortex continues its plunge southward, but the core of the cold wave will hit northern states the hardest.

The term polar vortex became a household phrase this winter as the United States started feeling its brunt, but it's a naturally-occurring event in the Arctic, where a cyclonic, high-altitude cold air flow circles from west to east above the North Pole. A polar vortex is also a naturally occurring event in Antarctica.

"The polar vortex is essentially a mass of very cold air that usually hangs out above the Arctic Circle and is contained by strong winds," said AccuWeather Senior Meteorologist Alex Sosnowski.

Weather experts say the United States is feeling the vortex because of rising global temperatures, reports U.S. News and World Report.  Since the Earth is getting warmer, the temperature difference between the Arctic and the lower states is narrowing, said John Holdren, director of the White House Office of Science and Technology Policy. As a result, the vortex pushes further south than normal.

The polar vortex's return will mean overnight lows approaching 30 below zero near the Canadian border, and will remain below zero during daylight hours for one or more days this week.

Elsewhere in the Northeast, the polar vortex won't bring subzero numbers, only below-average cold. Highs will be in the 20s and lower 30s — 10 to 20 degrees below normal. But wind chill factors will make it feel much colder, says AccuWeather.

"One reason for the cold blast carrying more weight than you might expect is the fact that the Great Lakes are largely frozen over," said Sosnowski. "The air will not moderate to the extent as if most of the lakes were not frozen. In addition, while the amount and extent of the snow on the ground has diminished, many areas north of I-70 have retained some sort of snow cover."

There will also likely be some fresh snow in the Midwest and Northeast, where last week's higher temperatures melted off a great deal of snow cover. There will be only about an inch or two of snow in those areas, but the Northeast, including the I-95 corridor from Washington to New York City, is being put on alert for more.

But there is a bit of good news where the polar vortex is concerned, reports The Washington Post.  The frigid air is not only dangerous to humans caught outside in it, but it also kills those pesky brown marmorated stink bugs that have invaded millions of homes in recent years.

Virginia Tech field researchers gathered stink bugs last fall and put them into ventilated foam insulation tubes to simulate the wintering locations of stink bugs, often homes' attics.

The bugs are able to change their proteins to keep their body fluids from freezing, but the researchers found that the subzero temperatures caused by the polar vortex killed the bugs.

As a result of the high kill rate, Virginia Tech entomology professor Thomas Kuhar Kuhar said, “There should be significant mortality of BMSB (brown marmorated stink bugs) and many other overwinter insects this year.”

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