"The FOMC statement falls into the realm of low probability high impact event – i.e. unlikely to surprise, but if it does, it has some obvious capacity to have considerable market fall-out. Watch for any changes to the prior statement that “the unemployment rate, though lower, remains elevated.” Janet Yellen in her semi-annual testimony watered down the FOMC view a little by saying “Even with the recent declines, the unemployment rate remains above Federal Open Market Committee (FOMC) participants’ estimates of its longer-run normal level.” Take this as one example of how to make a very mild shift in the post FOMC statement language, that at the margin will support the USD.
Since last year, the average absolute change in EUR/USD and USD/JPY on an FOMC day without a press conference has been 0.24% and 0.32% respectively, roughly a third of FOMC days when there is also a press conference. Since January 2013, on FOMC non-press conference days are remarkable for the how absolute average close to close changes in all of equities, bonds, and currencies resemble the average changes seen on all non-FOMC days.
In other words the FOMC without a press conference and just a formal statement has hardly contributed anything special to volatility for the past 18 months."