1917 was tied for 2nd coldest at BWI- 1989 was #1 by a pretty large margin.
The most frustrating Decembers were 2011 and 2012, which finished 16th and 11th, respectively. I hope we can torch our way to #1 but we'd have to put up a +9.0 departure to get hottest December ever (1931) so that's gonna be very hard.