Alright, I don't like to be that guy that always thinks that he's smarted than everyone else and likes to try to predict the next big market downturn. Nor do I like to be that guy that writes the previous sentence to feign humility all the while thinking he's doing God's work (Lloyd Blankfein). That being said, here's a chart with two distinct patterns that preceded a market crash. Make of it what you will.
We see price wedges at the two preceding market tops with RSI and volume trending down while it is forming.