I am not sure I understand the "2 Dimension" talk? Are they referring to 2 Vectors (Lets just say x and y) and alleviating z? Sorry for my ignorance, but my mind is pretty heavily wrapped around this one....
The way I took is that the clouds moved say, from the prespective of the observer, east to west and from closer to the ground to higher (or lower) to the ground but not away of towards the viewer -- or some variation on that theme.