A bitter Arctic outbreak has swallowed the Lower 48, bringing temperatures 30 to 50 degrees below average and wind chills as low as minus-60 to minus-70 degrees. Major cities such as Chicago and Kansas City struggled for days to make it above zero degrees. At one point, 30 states were under wind chill advisories or warnings. Now, a reinforcing shot of bone-chilling air - just as frigid as the first - is about to plunge south, and temperatures will plummet once again.