Today, Saturday, June 17, 2017, the Weather Channel presented its own hour-long documentary “Tornado: Inside the Vortex”.
Here’s an excerpt dealing with mutli-vortex tornadoes.
The documentary also explained the SLIM system for anticipating tornadoes: S for Shear (speed and height), L for Lift, I for Instability, and M for Moisture. Both cold fronts and ordinary surface low pressure systems can produce big thunderstorm complexes.
The documentary also showed the spot in Moore OK crossed by both the 1999 and 2013 tornadoes.
Here is some discussion of NOAA's discussion of the categories of risk for severe thunderstorms: marginal, slight, enhanced, moderate, and high.
Wikipedia attribution link for 2013 Moore OK damage, p.d., FEMA.