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Get ready for more volatile trading ahead

|Includes:SPDR S&P 500 Trust ETF (SPY)

Trading could get bumpy this week after last Friday's unusually becalmed mood in the markets. Be on the lookout for a spike in volatility -- on either the up or the down side.

In fact, Friday was so quiet that some market players are now expecting a surge in volatility this week now that the G20 is behind us and (apparently) brought a lot of feel-good consensus among the world's top economic powers with little real action behind it.

The much-anticipated G20 summit in Seoul ended with a somewhat bland statement that the "currency wars" are counter-productive even as a way for governments to preserve local growth at the expense of their neighbors. But in the lead-up to the summit, it looks like everybody got out of the markets. Traders on Friday confronted an eerily becalmed S&P 500 -- the SPY only moved 28 basis points between 10 a.m. and the close.

That "scary quiet" range, to quote one trader, turned out to be an N/R7 day, which means the broad U.S. market traded in its narrowest range in the previous 7 sessions. An N/R7 usually precedes an expansion of the range of volatility over the next few sessions, so today and tomorrow could get hot.

Disclosure: no positions
Stocks: SPY