Greece is roiling the currency markets with its debt-referendum plans. Here's how to trade the turmoil.

Just when you thought it was safe to go risk-on, what with the euro over 1.42 against the dollar, Greece up and announces a referendumon the latest debt deal. Rebecca Patterson, chief markets strategist for J.P. Morgan Asset Management, Institutional, says it's just one of many contributors to the volatility that's roiling currency markets - and sending the euro down around 1.36.

"The fact that the major volatility index is up 20% today tells me we're in a highly uncertain time," she told CNBC's Scott Wapner. She anticipates plenty of ups and downs in coming days, what with things like payroll data and a in the offing. Ultimately though, "the euro's heading lower over the next months and quarters," she says, to perhaps 1.30.

In Japan, meanwhile, the central bank is striving mightily to curb the yen's strength, but Patterson is adamant that "unilateral intervention does not work." She also thinks waning risk appetite could lift the Japanese currency.

Patterson wants to sell the euro against the yen, entering the trade at 107.00 with a stop at 109.25 and a target of 102.00.

You can watch the whole discussion on the videotape.

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