Volatility can grow very unexpectedly. For too long, the market is not allowed to fall.
This was already happening in the middle of the session yesterday.
Doubts about the trade deal persist.
https://www.reuters.com/article/us-usa-trade-china-timing/phase-one-u-s-china-trade-deal-may-not-be-completed-this-year-trade-sources-idUSKBN1XU2C7