UK & World News
Polar Vortex: Great Lakes Almost Fully Frozen
It looks more like a scene from Antarctica, but this striking image shows the United States' heavily frozen Great Lakes.
As the polar vortex bites the country for the third time in just two months, ice cover on the vast pools of water is at its highest level for four decades.
On average, around half of the surface freezes over during the bitterly cold winter months.
However, ice coated nearly 90% of the lakes on February 12 and 13 - only the fifth time it has extended beyond 80% in the last 40 years.
The unusually high ice coverage seen in the image from Nasa's Aqua satellite is caused by bitterly cold temperatures, coupled with extremely cold air that removes heat from the water as it barrels over the surface.
As the water temperature falls below freezing, a thin layer of ice develops at the surface, thickening when temperatures fail to rise.
The latest bout of winter weather has bought Arctic conditions to much of the United States.
It is triggered by the polar vortex - a rotating pool of cold, dense air held in place by a belt of strong winds.
That belt has loosened this year, letting polar air slip as far south as Alabama.
In Minneapolis, Minnesota, a city used to shivering through winter, temperatures fell to -4F (-20C) on Wednesday night, but even in cities on the east coast, such as New York and Philadelphia, Pennsylvania, the mercury plunged to 20F (-7C).
According to the Minnesota Climatology Working Group, this winter will be the state's coldest for 35 years.
Local meteorologist Paul Douglas told the Star Tribune newspaper: "Old Man Winter doesn't seem to care. He's stuck in a supernaturally persistent rut and the jet stream remains locked.
"Natural atmospheric variability, the natural ebb and flow of warm and cold, has been replaced by perpetually polar air, while much of the rest of North America runs a low-grade fever."
Alerts remain in place for parts of Minnesota, as well as Indiana, Wisconsin and Michigan, as a storm system tracks southeast across the country.
Sky News weather presenter Isobel Lang said there was "no real let-up" in sight, adding: "It does look as though it'll stay cold throughout the weekend, with snow at times, too."
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