Shares of Alcoa Corp (NYSE:AA) have an ugly head and shoulder pattern formation on the stock chart. While the head and shoulder pattern has not triggered yet, it is on the verge. If it triggers, there is huge downside to $23.00. The currnet price is $31.50. That means there is potential downside on Alcoa Corp of 27%. The key for investors is to watch for the neck-line to break. That is at approximately $31.00. Keep in mind, it needs to be a daily close below $31 to trigger. Once that happens, game on! Head and shoulder patterns are nasty and Alcoa Corp has a beautiful one.