Looks like the Polar Vortex is coming back for another visit:
The remainder or January is expected to be colder than normal, sometimes downright frigid.  The pattern is very similar to the pattern during the first week of January when temperatures plunged more than 20 degrees below normal in the so-called polar vortex event.   This time, the cold could stick around for a longer duration.

Temperatures should average well below normal starting around next Tuesday, lasting at least through the end of January.

http://www.washingtonpost.com/blogs/capital-weather-gang/wp/2014/01/16/return-of-the-polar-vortex-cold-at-times-downright-frigid-for-end-of-january-increasing-snow-chances/