The U.S. is off to its warmest year on record (through May), and this holds true in the Washington, D.C. area.
NOAA’s National Climatic Data Center (NCDC) has developed some rather astonishing graphs of year-to-date temperatures compared to previous years. They show all three local Washington, D.C. area airports - Reagan National (DCA), Dulles (IAD), and BWI - tracking warmest on record by a wide margin.
Through the first five months of the year, temperatures are running some 5-6 degrees above normal (DCA 5.4, IAD 4.9 and BWI 5.8 degrees) around D.C. For statistics wonks - these temperatures are about three standard deviations above normal (DCA 3.2. IAD 2.8 and BWI 2.9 sigma).
More than 100 cities identified by the NCDC are in a similar boat, including New York City, Minneapolis, St. Louis, Richmond, Raleigh, Providence, Philadelphia, Norfolk, Mobile, Memphis, Milwaukee, Little Rock, Houston, Detroit, Des Moines, Cleveland, Chicago, Buffalo, Boston and Atlanta.