6" for December puts me only a few inches below normal on the year. As of December 10th I was still running last place over the past 10 years, but the three storms bumped me over 2016 and 2017.
DCA's ASOS is on the east (river) side of the runways. It is not near the buildings. Now, the snowfall measurement location is a completely different issue, but they seem to have fixed that in the past 5 years or so.
After driving down towards the river, I’m shocked that DCA did get on the board. There is no sign at all that it snowed, other than the cars that came in from higher elevations.