I think it is more the longer term trends that we are looking at here, i'm not sold that the climate is not a factor. Looking at historical snowfall for DCA back to the late 1800s you can see a pretty consistent downward trend. Yes, some big years... But the recent "big hits" used to be the norm. Obviously there will always be ups and downs but the trend is definitely something to keep in mind.
dcasnow.pdf