2000-2005 had some very cold first weeks of December. At least at IAD, 12/1-12/7 this year was also colder than every first week of December in the 1980s and 1990s. In 1998, the average high between 12/1-12/7 was 73.4. In 1982 it was 63.1.
A random week obviously is not long enough of a period to make any meaningful historical comparison. But 12/1-12/7 this year was very cold for our area by any historical standard.