Just watched the radar loop of the Joplin storm and noticed something kind of interesting. As the parent supercell was moving through Joplin another supercell had quickly developed just to the south. This supercell quickly moved northeast and seemed to interact with the Joplin sup. The FFD on the northern edge of the southern sup may have helped to tighten up the RFD on the Joplin sup, and may have also helped tighten/funnel the inflow on the east/southeast side of the meso. That could explain why the thing exploded in intensity so quickly, and also why it only lasted 6-7 miles.
http://www.rap.ucar....e=23&duration=2
NOTE: The above radar loop will not be viewable after today, as it will fall off the 5-day archive.