Actually,
Skynet went operational on November 23, 1974. :lol:
The alternative theory is that we humans kept sending ourselves back and successfully defeating the machines, so instead of sending back Terminators, they began changing Earth's weather on April 21, 2011.
Interestingly, that's when the first round of super-massive storms wrecked havoc on the Southeastern states. Wednesday's tornadic slaughter of nearly 300 people was Round 1.