Heh. Looking at that map makes me think of the Blizzard of 1996. I was in my first year at Duke Law that winter and the storm walloped North Carolina. Durham County's roads didn't get cleared very quickly because the county's snowplow broke down. (That's right, "snowplow," singular.)
I don't know what source the iPhone weather app uses for its forecast. Mine is showing 2–4 inches of snow for Alexandria on Saturday and 16–20 inches on Sunday.