Jet Propulsion Laboratory in Pasadena has been tracking asteroids, both past and future. They know all the dates, locations, distances in their Near Earth Object Program clear out to the year 2100.
http://neo.jpl.nasa.gov/
Ummm, not quite all. Think of the earth as being in the center of a large dinner plate. The Jet Propulsion Lab is watching everything toward the outer edge of the plate, and about an inch above and below the surface of the plain. They do not have the resources or capabilities to watch what is directly above or below the plate. This is where the "close encounters" are reported after the asteroid or meteor passes. Until there are satellites with the capability of watching above and below, the Jet Propulsion Lab is working on a two dimensional view in three dimensional space. That's were the vast majority of asteroids and meteors are present, but it's one from the small fraction that'll probably get us.
Best advice... don't worry about it.