A massive swath of the country is already shivering through below-average temperatures, and meteorologists warn that things could get significantly colder in the days and weeks ahead. More than 170 million Americans are currently dealing with unusually frigid conditions, and the culprit is a displaced polar vortex that's parking some of the season's most intense Arctic air right over North America. Normally, the polar vortex, that ring of powerful winds high above the Arctic, stays strong and circular, trapping the coldest air near the poles and leaving milder weather for places farther south. But when it gets disrupted, things change fast. Here is what you need to knowIn the current setup, the vortex hasn't just weakened; it's been stretched out.