Market reactions after the US Federal Reserve decision could be volatile, as this is not a piece of numerical data. The language of the policy statement will need to be interpreted, so the near term reactions could be less obvious. To determine momentum and potential direction tomorrow, watch price activity in the 1570 area. This would confirm a false break of the latest "all time highs" and suggest further weakness. 1570 is the 38.2% Fib retracement of the rally from 1530 so a break here will remove some of the bias for buyers to enter in the short term.
Today we finished with negative sentiment and in my opinion there is a potential for more short selling tomorrow, when a potential euro interest rate cut could trigger selling through all the stock markets.