Often, there will be an energy transfer from a storm moving up west of the Appalachians to a secondary system along the East Coast. This is basically what will happen today and Saturday. One storm center will come into Tennessee and Kentucky, then there will be a new, more significant development along the Carolina coastline. The coastal storm is the one that is going to do most of the dirty work.
In most winter storms, the rate of snowfall varies at least to some degree hour by hour. There can be temporary lulls, and there can be times when it is snowing so hard that you can't see your hand in front of your face. Rate of snowfall criteria is shown below.
The storm that will hit the mid-Atlantic later today into Saturday morning will put down 1 to 2 inches of snow per hour at times, but probably not 3 or 4.
Those excessive rates are reserved for the meanest of winter storms. When it is snowing that hard, the house across the street completely disappears from view.
Story by AccuWeather.com Senior Meteorologist John Kocet.