Well I don't know what you mean by "severe polar vortex." The biggest threat of severe cold in North America and Europe comes with a weaker stratospheric polar vortex. Incursions of warmer air from further south can disrupt the vortex and send large masses of arctic air plunging south to give very cold weather. If the vortex is strong it will maintain its circular flow around the pole and keep the cold arctic air confined, giving us mild winters. As I've said before, beware of rambling popular science articles. Not sure how far ahead these sudden stratospheric warming events, giving us very cold weather, can confidently be predicted.