Well, I wasn't here for that event (was in northeast OH at the time), but locally DCA recorded I think 6.6" as I recall? Of course, that's DCA measuring. But many others in the metro area received a foot or more even, before sleet and ice moved in. The storm was obviously "special" on the large scale given the wide area it covered, with anything from severe weather to blizzard conditions and feet of snow (48" in Syracuse, something like that!). Not to mention unreal heavy snows in AL/GA...in March. From what I've read about that storm for the local DC-Balt area, it still met blizzard condition criteria. For a mid-March storm in this area, that's quite impressive. There was also some pretty deep cold for a couple of days after that (true for much of the eastern 1/4 or so of the country). So maybe not a HECS in the metro areas just going by snowfall amount...but definitely taking into consideration everything else (wind, cold, snow, and ice).
In northeast OH where I was, we were on the western edge of that storm and still had blizzard conditions. About 8-12" snow locally and gusty winds, along with temperatures in the teens or low 20s.
Not sure what the pressure was in DC (DCA), but I recall the central pressure of that storm was on the order of ~960mb at its peak. To compare and give an idea of just how big that is, the Ohio Blizzard of 1978 (Jan. 26-27, 1978), which I lived through, went right through Cleveland. KCLE recorded their lowest pressure on record, 28.28" (957mb) as it went through. That may still stand as the 2nd lowest non-tropical storm pressure in the continental US. We didn't get extremely heavy snowfall from that...7" at KCLE, a bit more west...but 40+ MPH winds and gusts pushing 100 MPH near the lakeshore, along with temperatures in the single digits made it extremely dangerous (temps fell from mid 40s to the teens in about 2 hours, during the pre-dawn hours, and continued falling into the single digits for the rest of the day). That snow fell on top of about a foot of older crusty snow that already was on the ground.