During the month of January 2014, the continental United States experienced several bouts of extremely cold air that moved southward from the north polar region. The frigid temperatures made news headlines as they caused conditions dangerous to health and safety. The polar vortex, a circulation of strong upper-level winds that normally surround the northern pole in a counterclockwise direction, tend to keep frigid air locked in the Arctic. This pattern became distorted, due in part to a persistent high pressure system over the eastern Pacific Ocean that forced the jet stream southward over the continental United States allowing the cold polar air to spill southward.
This visualization, made with data acquired January 1st through 29th from AIRS, the Atmospheric Infrared Sounder on NASA's Aqua satellite, shows the difference from the average air temperature near Earth's surface. Areas from yellow to red are warmer than average and areas from green to purple are colder than average. Note that Alaska was experiencing warmer than normal temperatures while the cold air mass moved south over the contiguous United States.