The last six times we had a scheduled FOMC meeting, the market typically responded in joyous fashion, closing in positive territory five times with an overall average of a huge +2.4%.
But a cruel fact of life is that the hangover is never as much fun as the party, and over the next two days the S&P was positive only one out of the six, with an overall average of -1.6%. It would average -2.8% without including that one winning trade, which happened to give back all its gains and then some within four more sessions.
We've gapped up by +1% or more the morning of a scheduled meeting only twice before, on 03/18/08 and 01/28/09. Both times, the S&P managed to add an additional +1% or more during the day. But the harder you party, the worse the hangover (usually), and the next day the S&P was lower by more than -2.5% both times.
Even if we relax the gap and only look for +0.5% openings, the pattern is pretty much the same. The S&P closed higher than the open 9 out of 10 times by an average of +1.2%. But by two days later, the S&P showed a positive return only 1 out of the 10 times with an average of -1.7% (and that one positive outlier gave back its gains the following day).