I live just north of DC in the suburbs. We got about a foot of snow, but today is in the 40s and it is melting nicely. The highways are all clear and most of the main roads are clear. It's the neighborhoods that are still being dug out.
That said, we are expecting about an inch of snow to fall overnight and into tomorrow morning, so the roads could be a little dicey.
However, I am still planning on going tomorrow. The arboretum is just off a main road in DC, so I don't anticipate any real problems getting there.
--Stephen