The researchers found that ordinarily, the counter-clockwise flow of air that defines the polar vortex helps keep colder air near the Poles. But when sea-ice north of Scandinavia and Russia melts, the now ice-free ocean releases more warmth, which can rise as far as 18 miles into the stratosphere. It weakens that counter-clockwise circulation, allowing more cold air to escape further south. That leads to those unusually colder winters. The study authors found that they could attribute many of the coldest winters over the past 40 years to the weakening of the polar vortex.
A warming Arctic can actually make our winters colder - Popular Science