All tornadoes are spawned from a parent supercell, but not all supercells produce tornadoes. Damage from the 1999 F5 tornado that struck Moore, Oklahoma. Photo courtesy NOAA. Dr. T. Theodore ...

It was tracking a tornadic supercell into Mercer ... it was reclassified as an F5. That scale would later become adopted nationwide as the benchmark for tornadoes.

A supercell is a highly organized thunderstorm with some components that set it apart from other "garden variety" thunderstorms. Supercells have the capability to produce tornadoes, damaging hail ...