The weather issue has been discussed extensively, however, the electrical power issue has not. The stage canopy collapsed at 8:49 PM, yet the timeline shows that the power wasn't cut to the stage for almost another half hour. There were hundreds of people climbing in, under, and on that aluminum structure and the power was still HOT! Truly, someone was asleep at the switch. Fortunately, no one was electrocuted. Crushed, yes, but electrocuted, no.
How come the power wasn't killed BEFORE the canopy blew down? At the time the storm was identified to contain rain, hail, lightning, and wind (most summer storms contain these four elements, so this isn't 'unexpected' or 'freakish'), the lighting and sound power should have been disconnected, and the winch power left on-line until the canopy was safely brought down to the stage level. This should have happened waaay earlier than the timeline shows.
NEWS FLASH: Water and Electricity and Aluminum structures are not a good mix. Add people to that and you have a recipe for further disaster.
Event Planning: When you are doing outdoor shows there should always be someone at the power source so that power can be shut-off in the event of an emergency. The power source and disconnect location should be located outside of the crash radius of the structure so that the workers there can operate the controls / disconnects and so the falling structure can't bury the one thing you must get to if an incident like this occurs.