This is such an uncertain market. On the days when the market is weak, the bargain hunters show up. When it's strong, the nerves take over and the bulls bail out.
I don't see how that kind of volatility ebbs until inflation gets back to about 3% and trending lower. The market is cautiously optimistic about inflation but that 'cautious' thinking doesn't lend itself to the kind of conviction to sustain a bull market unless the data cooperates.
Obviously though, data has ebbs and flows. Today's initial jobless claims data is certainly something to worry about and corporate comments have been positive.
As for the dollar, the London fix could also be having an effect.