The U.S. Midwest and Northeast were braced for dangerous subzero temperatures this week, as the polar vortex was set to blast arctic conditions unusually far south, the National Weather Service said on Monday. The system was set to extend from the Dakotas through New England, with Chicago expecting temperatures to plunge as low as -25 degrees Fahrenheit (-32 Celsius) overnight Tuesday into Wednesday, the weather service said. The polar vortex – the frigid winds that circulate around the North Pole – is extending further south into the Upper Midwest, said weather service meteorologist Brian Hurley.
