Continued...

It appears the announcement itself wasn't known in advance as far as timing today, but it does appear the action of the policy announced has been known. Global intervention like that isn't decided on in a day, there's a lot that goes in to something that big, thus these two charts of the SPY...

 1 min intraday suggets timing of the announcement wasn't known-don't assume this is a cake walk, there will almost surely be denials causing market volatility.

The 60 min SPY chart has been in leading position since the bear pennant (yellow triangle), but look at the leading positive since the market pulled a head fake and hit the lows (which technical traders assumed would be the next leg down0, that divergence is amazing and starting to bleed to the daily chart.