For BWI, using the 1981-2010 normals, I think 1/26/1950 might hold the record for biggest positive departure- I calculated a +37 departure for that day.
12/22/2013 was a +32 departure and the next best one I know of.
For negative departure, I got -37 for 2/10/1899 and -33 for 1/19/1994.
There may be others but that's the best I'm aware of.