The two jets may've been closer than previously thought
According to this CNN article, the two planes may have been as close as 90 seconds from one another, much closer than previously thought. I've seen demonstrations where the vortices from wake turbulence can last well over a minute, and that was from a small WWII fighter. The vortices from a heavily loaded 747 can be very powerful. If the winds were fairly calm, they might've stayed in the area for some time. If this turns out to be the cause for the crash, it may be unprecedented.