U.S. Postal Service letter carrier Jamie Jasmon struggles through snow and below zero temperatures while delivering the mail Monday, Jan. 6, 2014, in Springfield, Ill. A whirlpool of frigid, dense air known as a "polar vortex" descended into much of the U.S. and plunged temperatures to record lows.

Seth Perlman / AP

U.S. Postal Service letter carrier Jamie Jasmon struggles through snow and below zero temperatures while delivering the mail Monday, Jan. 6, 2014, in Springfield, Ill. A whirlpool of frigid, dense air known as a "polar vortex" descended into much of the U.S. and plunged temperatures to record lows.