I'd say that's over two inches, probably about three now. I put it at about an inch an hour over here, and the snow's showing no signs of stopping.
This is an hour's worth of accumulation, mind you. It started snowing when Lyssa and I were on our way home and hasn't stopped yet. While stopped at a light, we saw a bolt or two of lightning streak across the sky, and our return home was hearlded by thunder.
Yes, DC is known for occasional thundersnow storms.