According to the U.S. Geological Survey, "The flooding around Atlanta this week is one for the record books. The rivers and streams had magnitudes so great that the odds of it happening were less than 0.2 percent in any given year. In other words, there was less than a 1 in 500 chance that parts of Cobb and Douglas counties were going to be hit with such an event."
The "1 in 500 chance," translated in terms of years means that a flood of that extreme would likely occur once every 500 years. One expert, taking into consideration the level of flooding that occurred at Clarkdale Elementary, stated that he thought it was an event even more rare than once every 500 years.
In my world, this was a local event and yet I still can't believe it happened.